INTRODUCTION

The successful launches of Chandra and XMM-Newton represent major landmarks in the field of X-ray astronomy. Leicester had a hardware role in both missions. In the case of Chandra our involvement was in the High Resolution Camera and for XMM-Newton, a PI role for the EPIC instrument. It is a matter of great satisfaction to report that both instruments are performing extremely well in space. XMM-Newton and Chandra are highly complementary in terms of their capabilities - Chandra delivers X-ray spatial resolutions comparable to high quality optical ground-based images, whereas the high throughput and broad-band coverage of XMM-Newton provides an unsurpassed facility for X-ray astrophysical spectroscopy. The impact of these new generation missions is being felt across the broad range of high energy astrophysics from Galactic studies, through normal and active galaxies, to clusters and deep surveys. As an example, we have used Chandra to image starburst and other nearby galaxies. The picture which is emerging is one of wide diversity and complexity. In nearby galaxies we see extended soft X-ray emission from outflowing winds and expanding bubbles, and in hard X-rays a component possibly analogous to that observed along the Galactic ridge. The discrete source populations can now be readily separated into binaries and supernova remnants. XMM-Newton is revealing the true spectral complexity of cosmic X-ray sources. For example, in active galactic nuclei, different continuum components arising from reprocessing and reflection are apparent along with a wealth of emission line and edge features. In particular the important diagnostic capacity of the iron K alpha line has been emphasized by recent observations. Often in science a rapid increase in perceived complexity is a precursor to a rationalization or revision of the standard model, which in turn is accompanied by a deeper understanding of the physical processes involved. X-ray astronomy as a whole may now be entering such a phase, and through our own research programme we are well placed to contribute to this broad front advancement of the field.

Leicester is the host institute of the XMM-Survey Science Centre (SSC). The SSC is responsible for the science analysis software design and the pipeline processing of all XMM data. During the reporting period, the SSC programme to follow-up the X-ray source populations detected serendipitously in XMM EPIC images has come into full operation. This project involves gathering optical/IR observations, using a wide range of major worldwide facilities. Related to this activity is the successful collaborative bid for International Time on the telescopes on the Canary Islands (the "AXIS" programme).

We have continued to use other satellites, e.g. HST/STIS and FUSE for white dwarf studies, and ASCA and Beppo-SAX, for AGN. In conjunction with our X-ray studies we have used optical telescopes (WHT) to investigate the environments of an intriguing class of ultraluminous X-ray sources, that appear to be binary systems, and UKIRT to quantify the star forming characteristics of X-ray bright starburst galaxies.

The group has also played a leading role in a number of projects in the area of e-science. It continues to host the Leicester Database and Archive Service (LEDAS) and is now a leading member of the AstroGrid consortium. The AstroGrid project, which was recently given the go-ahead to commence its work, aims to provide substantially improved accessibility to, and interoperability between, the very large datasets which are soon to become available.

This report also coincides with the first period since the group's space projects and laboratory programmes were re-located in the new laboratories and facilities in the Space Research Centre. The move has produced very positive results with added cohesiveness in the experimental programmes and increased exchange of information and data between the various project teams. The successful launches and commissioning of Chandra and XMM-Newton are major highlights of the reporting period, representing the culmination of a decade of painstakingly careful development, test and calibration of the space instrumentation. This is now delivering the promised astrophysical research products to the wider national and international astronomical communities. In the same period, we have had major successes in establishing a key role in NASA's MIDEX SWIFT mission to study Gamma Ray Bursts and their afterglows, and in the space system management and key development tasks in Beagle 2 - our first excursion with a Planetary mission.

Steady progress has been made in all branches of the laboratory research programme, but the notable success has been the maturing of microchannel plate X-ray optics techniques, to the extent that it provides the core technology of the Leicester-led X-ray All Sky Monitor - Lobster - recently accepted by ESA for Phase A study for flight as an attached payload on the International Space Station.

The leading role played by the University in proposing and then actively contributing to building the National Space Centre Millennium project provides a new and totally novel showcase for our, and PPARC's, programmes in space science and astronomy. By the first weekend in September, 100,000 people had visited the NSC since it opened on 30 June 2001. This is "science outreach" in the true meaning of the term.

ASTROPHYSICS HIGHLIGHTS

2.1 Introduction

Astrophysics research at Leicester utilizes data collected across the electromagnetic spectrum, from the radio through the IR and optical/UV to the X-ray band. Recently much of our programme has concentrated on the exploitation of the new X-ray observatories, Chandra and XMM-Newton. We have benefitted from early access to XMM-Newton data from the Performance Verification (PV) and Calibration (CAL) phases of the mission, as well as early observations obtained with XMM guaranteed time (GT) afforded to the XMM EPIC and XMM SSC teams. The new observatories, with their remarkable capabilities, are providing a major impetus to the field of X-ray astronomy. The impact of these missions on our own programme is apparent in many of the topic areas discussed below and, increasingly, is reflected in our publication record.

2.2 White Dwarfs

M.A. Barstow, N. Bannister, M. Burleigh

2.2.1 Composition and evolution of hot white dwarfs and their progenitors

A study of the hottest known white dwarfs and their immediate progenitors, the old central stars of planetary nebulae (CSPN), has been carried out with HST/STIS, the Far-UV Spectroscopic Explorer (FUSE) and ground-based telescopes. To complement these observations we have developed new stellar atmosphere models accommodating higher temperatures and including higher ionization stages of important heavy elements. Using these we can now make self-consistent measurements of T and log g, taking into account the composition of the white dwarf atmosphere. For the first time we have adopted a completely objective approach by using a spectral fitting procedure involving a chi-squared minimisation technique, which allows us to determine formal errors for measured abundances and, consequently, make statistically valid comparisons of the measurements of individual stars in the sample. As part of this project, we have also obtained the archival data of many cooler stars and reanalysed these with the new models for internal consistency. So far we have studied 20 stars in detail, but this project is a continuing one, with much data (particularly from FUSE cycle 2) to obtain and/or analyse.

2.2.2 Temperatures of the hottest white dwarfs

Earlier work has shown that the temperature inferred for the hottest ( T ~ 50,000 K) white dwarfs is very sensitive to the modelling approach, particularly that used to analyse the Balmer line profiles. For example, a significantly lower temperature is obtained if the models include appropriate abundances of elements heavier than H or He, compared to a pure H model. The most extreme effect is in the very hottest white dwarfs; an illustration is provided by WD2218+706 for which the best current value of surface temperature is nearly 20,000 K cooler (at 57,400K) than the previous estimates [281]. As an old CSPN, WD2218+706 is an enigmatic object. The HeII 1640Å line is visible in the STIS spectrum which represents the first detection of trace He in an apparently isolated DA white dwarf. However, the surface gravity of the star, and the resulting estimated mass of 0.41 solar masses, shows that the star lies on the boundary of normal post-AGB tracks and binary evolution routes (Figure 2.2-1). Hence, it may provide an important observational constraint on the lower mass limit for post-AGB evolution, if it is indeed an isolated object. A search for a possible companion, to confirm or deny this status, is now important.

Figure 2.2-1. T_eff versus log g diagram showing the location of WD2218+706 (marked as DeHt5) compared to single star (with M >= 0.524 M₀) and binary evolution predictions (with M <= 0.414 M₀).

2.2.3 Circumstellar material in hot DA white dwarfs

An important result of our HST/STIS observations of hot DA white dwarfs is the identification of multiple absorption components in one or more of the strong resonance absorption lines associated with the stellar photosphere (e.g. CIV, SiIV, NV, and OV) [279]. In most of the stars observed the components are blue-shifted and present in at least CIV (Figure 2.2-2). While no consistent pattern has yet emerged from the small number of spectra available, the material may be from recent or ongoing mass-loss or a remnant from a now dispersed planetary nebula. In some stars, such as the well-studied prototypical hot DA G191-B2B, the blue-shifted features are barely resolved by STIS and were not resolved in earlier IUE or GHRS observations. Hence, the abundance of photospheric carbon, determined from what are now known to be weaker photospheric lines, is much lower than previously supposed. As a result, all similar pre-STIS measurements of hot DAs are now suspect. We are investigating the use of FUSE spectra to provide complementary abundance data from non-resonance transitions, but it may ultimately be necessary to obtain new STIS spectra of many stars.

Figure 2.2-2. STIS spectra of REJ1738+766, showing the blue-shifted components of the CIV doublet.

2.2.4 The pattern of heavy element abundances in hot DA white dwarfs

We have carried out a systematic series of abundance measurements of hot DA white dwarfs in the temperature range 20,000-75,000K, combining all the available spectra from both our own observation programmes and the far-UV archives with new model calculations [283]. In particular, we have addressed the abundance patterns for the hottest stars for the first time, showing that they are similar to objects like G191-B2B. The abundances observed in the cooler white dwarfs (T<50,000 K) are something of a mystery. Some of the patterns can be explained by self-consistent levitation-diffusion calculations, where the radiation pressure supports certain elements against the downward pull of gravity. However, there is then a problem in understanding the appearance of apparently pure H atmospheres and the presence of heavy elements in cool DAs, where the radiative levitation mechanism is no longer effective. In the latter case, the stars may be undergoing active, low-level, accretion. Note that there is strong evidence that the 35,000K DA star GD394, which has the highest Si abundance known in any white dwarf, has a companion. Hence, the presence of heavy elements in the cooler DAs may be a signature of binarity, where the companion is too cool/low mass to detect in visible band spectra.

2.2.5 Far UV spectroscopy and imaging of Sirius-type binaries

Sirius-like binary systems consist of a white dwarf plus a main sequence, or slightly evolved star, of spectral type B-K. In most cases the white dwarf is undetectable optically because its flux is completely swamped by the bright primary. Over 20 new systems were identified in the 1990s through the detection of the white dwarf's EUV and soft X-ray flux. Sirius-like binaries are of astrophysical importance since they can be used to investigate the relationship between the mass of a main sequence star and its white dwarf progeny. Potentially they can also be used to place observational constraints on the theoretical white dwarf mass-radius relation.

Burleigh & Barstow [35] identified a hot white dwarf companion to the B9.5V star 16 Dra (HD150100), using spectra obtained with EUVE. White dwarf companions to B stars are of significant importance since they must have evolved from massive progenitors, perhaps close to the theoretical 8M₀ maximum mass for all white dwarf progenitors (and, therefore, the minimum mass for producing a Type II supernova through core collapse).

Barstow et al [12] attempted to resolve a number of Sirius-like binaries in the ultra-violet using the Wide Field Planetary Camera 2 on the Hubble Space Telescope. Out of 17 targets observed, 8 were successfully resolved. Although most of the implied orbital periods are hundreds of years, in at least three cases, 56 Persei (Figure 2.2-3), Zeta Cygni and RE J1925-566, it should be possible to detect orbital motion within a few years, yielding dynamical masses for the white dwarf components.

Figure 2.2-3. HST WFPC2 image of 56 Per in the far-UV. The image is 10x10 arcsec². The Aa-Ab part is the F4V primary and its WD companion. The previously known visual companion (B) is also resolved into two components.

2.2.6 Measuring T and log g in Sirius-type binaries

Since the white dwarfs in Sirius-type binaries are unobservable optically, we have previously been unable to accurately establish their temperatures, surface gravities and masses by the usual method of fitting model atmospheres to the optical H Balmer absorption lines. The advent of far-UV spectroscopy from 900Å to 1200Å with the FUSE satellite, covering the entire hydrogen Lyman series, allows us a first opportunity to determine precisely these fundamental parameters for the white dwarfs in these binaries. We have programmes in FUSE Cycles 1 & 2 to pursue this goal.

While the Balmer line technique is well-established, only a few Lyman series spectra have been available to make equivalent measurements. An important precursor to using the Lyman lines, particularly for those binaries where the white dwarf Balmer lines cannot be observed, is to establish that this technique gives reproducible results which are consistent with the Balmer line measurements of isolated stars. We have carried out a survey of all the available Lyman line data from past missions such the Hopkins UV Telescope (HUT) and Orfeus, together with early release data from FUSE [284]. We have developed a systematic technique for measuring T and log g along the lines of that established for dealing with Balmer line data, but taking into account the fact that the wings of the Lyman lines often overlap significantly. There seems to be good overall agreement between the Balmer and Lyman line measurements, although significant differences are found for a few stars, possibly arising from systematic effects in the observation and data reduction process. Provided these can be adequately controlled, the Lyman line technique does give valid results. Initial use of the Lyman series lines to study the white dwarfs in our sample of Sirius-like systems has been spectacular. Burleigh et al (2001, MNRAS, in press) have shown that the white dwarf companion to the bright A1 giant Beta Crateris possesses an unusually low mass, and has almost certainly evolved through binary interaction. This system could be a long sought remnant of Algol-type evolution.

2.2.7 Photospheric nickel in the hot DO white dwarf REJ0503-289

Nickel is often detected spectroscopically in the atmosphere of hot H-rich DA white dwarfs and is always found along with iron. However, it has not been detected in a helium-rich DO white dwarf until recently. Our HST/GHRS observation of REJ0503-289 presents the first evidence for the direct detection of Ni in the atmosphere of a He-rich object [13]. Intriguingly, Fe, which is observed to be more abundant than Ni in the hot DA stars, is not detected. The upper limit to the abundance of Fe in REJ0503 implies an Fe/Ni ratio a factor of 10 lower than seen in the H-rich objects.

2.3 Stars and Stellar Clusters

J.P. Pye, K. Briggs, T. Roberts, R.S. Warwick

2.3.1 Hyades-age open clusters

The paradigm that younger stars spin faster and hence support enhanced coronal activity has been challenged by the measurement of very disparate X-ray luminosities for stars in Praesepe and the Hyades which are both intermediate age (~ 600 Myr) open clusters. The suggestion is that other factors, perhaps metallicity or evolutionary environment, also have a significant effect. We have studied deep ROSAT HRI pointings of the two other Hyades-age clusters closer than 800 pc, NGC 6633 and IC 4756, and have proposed identifications or classifications for the detected X-ray sources on the basis of published membership lists, X-ray to optical flux ratios and optical colour-magnitude diagrams. We have found 6 potential new members of NGC 6633, and 4 in IC 4756. From simulations based on the Hyades, it seems that all of the above clusters contain similar proportions of X-ray-emitting stars, although there is considerable uncertainty in the richness of NGC 6633 and IC 4756. In particular these latter clusters may lack the highly-active F and G stars found in Praesepe and the Hyades [32].

2.3.2 Pleiades-age open clusters

The Pleiades is probably the best known of all open clusters. The X-ray activity of its members is typically an order of magnitude higher than that of the Hyades, commensurate with the difference in the cluster ages (~ 100 Myr as opposed to ~ 600 Myr for the Hyades). We are carrying out a detailed study of the Pleiades system using XMM-Newton. The unparalled sensitivity of XMM-Newton allows us to detect X-rays from much later type cluster members than has been possible hitherto. The 40 ks XMM-Newton observation (Figure 2.3-1) is centred on the brown dwarf candidate Teide-1 and we can put very tight constraints on the level of its X-ray emission. We are also performing spectral and timing analysis of a number of bright, flaring coronal sources in the field.

NGC 2516, often known as "the Southern Pleiades", is an important Pleiades analogue as its low metallicity allows investigation of the effects of chemical composition on coronal activity. Several observations of the cluster have been made by XMM-Newton as part of the process of calibrating the EPIC metrology. First results have shown the photometrically-selected dG and dK members to be less luminous than those of the Pleiades, while the respective luminosity functions of dM members are indistinguishable [131]. Analysis of variability over timescales of weeks and months, as well as hours, will be used to compare the observed flare frequency with that found in our Pleiades observation.

Figure 2.3-1. A three-colour XMM-Newton EPIC image of the Pleiades

2.3.3 AB Doradus

AB Doradus is a very active, nearby, young dK star, which was observed by XMM-Newton during the performance verification phase of the mission (Figure 2.3-2). Time-resolved spectroscopy demonstrated significantly sub-solar metal abundances throughout, but with a perplexing increase by a factor ~3 apparent in the early flare phases. In decay, the temperature of the flare component does not fall below that of the hotter quiescent component, indicating that the plasma in the flaring loops is maintained at high temperatures long after the flare peak. Modelling of the flare decay by A.Maggio (Palermo) has suggested heating continues through the course of the flare, and determines the semi-length of the magnetic loop to be ~0.3 stellar radii. High resolution spectroscopy with the XMM RGS shows that the average density of the cool plasma did not change during the course of the flare [64].

Figure 2.3-2. EPIC pn light curves of AB Doradus demonstrate the correlation of hardness ratio with count-rate, indicating that the coronal plasma gets hotter not only during pronounced flares but also during much smaller amplitude variations.

2.3.4 ROSAT Medium-Sensitivity Galactic Plane Survey

Flux-limited X-ray surveys are important both in the study of source populations and in the identification of interesting objects. The ROSAT PSPC medium-sensitivity survey in the third Galactic quadrant (180^o < l < 280^o, Figure 2.3-3) probes the Galactic plane to a level an order of magnitude deeper than previous surveys, having a median limiting flux of ~1.3 x 10^-14 erg cm^-2 s^-1. A total of 93 X-ray sources were detected in a sky area of 2.5 sq.deg. We have performed cross-correlations with optical and near-infrared (NIR) catalogues to find potential counterparts to these sources, and used X-ray to optical flux ratios, together with optical and NIR colours to classify them. The majority (~70%) of the sources have stellar coronae counterparts, as is the case in shallower surveys of the plane. Comparison of the measured number-flux relations with predictions of Galactic (stellar) and extragalactic populations supports the view that the population of young stars in the plane is denser than previously thought [312].

Figure 2.3-3. A comparison of the number-flux relation for X-ray sources found in the ROSAT medium-sensitivity survey with the relations predicted by various models of stellar and extragalactic source populations in the galactic plane.

2.4 Cataclysmic Variables and Related systems

P. J. Wheatley, J.P. Osborne, M. Burleigh, D. Baskill, S. Poulton, J. Pye, K. Sohl, M.G. Watson, R West

2.4.1 A new interpretation of the X-ray spectra of symbiotic stars

Symbiotic stars are binary stars in which usually a white dwarf accretes from the wind of a red giant. Their X-ray spectra are dominated by distinct soft and hard X-ray components (and sometimes a third "supersoft" component not discussed here). Previous work has attributed the hard component to accretion power at the white dwarf and the soft component to shock heating in collisions between the stellar winds of the two stars. Reanalysis of the published ASCA X-ray spectrum of the bright symbiotic star CH Cyg shows that the entire spectrum can instead be understood as a single emission component (Figure 2.4-1). The apparent separation into two components is the result of strong absorption by a partially-ionized medium, probably the wind of the giant. The single emission component is perfectly consistent with that of an accreting white dwarf, and this study shows that X-ray data in general have not so far provided evidence for colliding winds in Symbiotic Stars.

Figure 2.4-1. Left: ASCA X-ray spectrum of the symbiotic star CH Cyg with apparently distinct soft and hard X-ray emission components. Right: The model spectrum of Wheatley (2000) which yields an excellent fit to the ASCA spectrum. A single emission component is absorbed by a partially-ionized medium that cuts deeply at intermediate energies but allows soft photons to leak through.

2.4.2 Evidence for a substellar secondary in a cataclysmic binary

Further work on the optical spectrum of EF Eri has yielded the first clear evidence of a substellar companion in a cataclysmic variable. EF Eri is usually one of the brightest cataclysmic variables but optical observations during the 3.6m ESO telescope captured the source in a low-state in which it was five magnitudes fainter than normal (see Figure 2.4-2). The new work focuses on the absence of any features attributable to a secondary star, even when the accretion luminosity is dramatically suppressed. The observed spectrum is consistent with that of a cool (9500K) white dwarf only. Beuermann et al [21] show that a companion as faint as spectral type M9 would have been apparent in the spectrum, and that the secondary must therefore be a cool brown dwarf. This observation places unique constraints on the evolutionary history of EF Eri, which must have either just passed through the period minimum of cataclysmic variable stars or started mass transfer from an old brown dwarf secondary.

Figure 2.4-2. The low-state spectrum of the cataclysmic binary EF Eri, taken at the 3.6m ESO telescope.

2.4.3 XMM-Newton observations of OY Car

Results from early XMM-Newton observations are demonstrating the power of its large effective area. The first observation of a dwarf nova, OY Car (Figure 2.4-3), has allowed us to resolve the ingress and egress of an eclipse in such a system for the first time [114]. These measurements allow us to constrain the masses of the white and red dwarfs to 0.9-1.1 and 0.08-0.11 solar masses respectively.

A surprise from these observations was the discovery of modulation, predominantly in softer X-rays (Figure 2.4-4), at a period of ~2240 seconds. This result clearly points to OY Car containing a magnetic white dwarf. The predominantly low energy modulation and the P_spin/P_orb ratio are typical of short period intermediate polars, adding weight to a classification that nevertheless needs confirmation.

Wheatley & West have analysed these data further and show that the X-ray eclipse ingress/egress is faster than that observed in the ultraviolet (30+/-3 s as opposed to 43+/-2 s). Since the ultraviolet variation is attributed to the white dwarf this implies that the X-ray emitting region is smaller than the white dwarf, and not larger as was previously believed. This difference can be explained naturally if the X-ray emission is confined to the equator of the white dwarf. This suggests the X-rays arise in a narrow boundary layer between the accretion disc and white dwarf, and that the emitting region cannot extend substantially above the white-dwarf surface or out of the orbital plane.

Figure 2.4-3. The XMM B, UVW1 and X-ray eclipse profiles of OY Car.

Figure 2.4-4. The 2240 second modulation of the X-ray flux of OY Car, leading to its proposed classification as an intermediate polar.

2.4.4 Studies of cataclysmic variables using archival data

Work with older X-ray datasets continues to yield interesting results. Ginga and ASCA X-ray spectra of the intermediate polar V1223 Sgr [18] have been used to explore the multi-temperature emission and the reflection components modified by the multi-column ionized absorption expected in magnetic cataclysmic variables. A spatially resolved model was constructed and fit to phase resolved spectra yielding a white dwarf mass of 0.87+/-0.15 solar masses.

As part of a systematic study of non-magnetic cataclysmic variables with ASCA, the dwarf nova Z Cam has been observed in outburst and quiescence [285]. The complex emission spectra reveal high absorption in both observations. Interstellar absorption to this object is well determined at 4x10¹⁹ cm^-2, whereas the X-ray spectra show 8x10²¹ cm^-2. An interpretation is that the absorption occurs in a partially ionised medium identifiable as a disk wind. X-ray observations are well suited to the study of the so-far poorly understood disk winds, and this first result shows significant promise for the future.

A search through the ROSAT Wide-Field Camera archive has turned up remarkable behaviour in two interacting binary stars. The dwarf nova SW UMa was observed in the very early stages of a superoutburst [292]. Such observations are very rare because of the unpredictable nature of dwarf nova outbursts. Only two partial superoutbursts have ever been observed before in the extreme-ultraviolet. The extreme-ultraviolet flux might be expected to stay high throughout the optical outburst, but remarkably the WFC count rate fell sharply throughout the observation. This result has still to be understood in terms of mass transfer through the accretion disc.

In the second case a previously unrecognised observation was found of the extreme-ultraviolet transient REJ1255+266 [160]. This object was originally discovered with the WFC through its remarkable extreme-ultraviolet outburst at which time it was in decline. The new observation was made four days before the discovery observations, and showed the system to be undetectable. This additional constraint rules out the previously popular explanation for the outburst (a superoutburst of a WZ Sge system). Most likely this was a short outburst of a WZ Sge system, even though such events have never previously been unambiguously detected.

2.5 Supernova Remnants

R. Willingale, N. Schurch, R.S. Warwick

2.5.1 The Crab Nebula

The Crab Nebula is the remnant of the historically recorded supernova of AD 1054. It is powered by a 33 ms pulsar, which injects highly relativistic electrons into the central nebula. As these electrons diffuse outwards through the nebula and its magnetic field they emit energy through synchrotron radiation and produce a very broad-band, radio through to X-ray, continuum. In the X-ray band the bright, stable, featureless nature of Crab's spectrum make it an ideal calibration source, which is invariably targeted by all new missions.

The Crab Nebula was observed by XMM-Newton early in the PV/CAL phase of the mission [161]. To accommodate the high count rate, the EPIC MOS instruments were operated in a refresh frame store mode, in which the frame exposure time was just 200 ms. Figure 2.5-1 shows the resulting image. The data accumulated from the full nebula provide a very high precision count rate spectrum. The spectrum from 1.5 to 5.5 keV has proved particularly valuable in the fine adjustment of both the detector quantum efficiency and the mirror reflectivity.

As is evident in Figure 2.5-1, there are significant X-ray spectral variations across the nebula. The Crab pulsar and its surrounding torus exhibit the hardest spectra with power-law indices of Gamma = 1.6 and 1.8. In contrast, the jet and outer reaches of the nebula are significantly softer with Gamma = 2.1 and 2.3 respectively. These results constrain the transport and lifetime of highly relativistic electrons in the nebula. The huge number of recorded counts also allows a detailed examination of the soft X-ray absorption due to cool gas in the foreground of Crab. Absorption edges due to oxygen, iron and neon are clearly identified in the X-ray spectrum (see Figure 2.5-2) from which we infer an underabundance of oxygen and iron by a factor of 0.63+/-0.01 compared to the solar norm. The measured column density is N_H = 3.45+/-0.02 x 10²¹ cm^-2 with no evidence for any significant variations in this value across the face of the nebula.

Figure 2.5-1. X-ray colour image of the Crab Nebula in 1 arc seconds pixels. The colour coding of surface brightness and photon index is shown in the lower panel. The white contour encircles the region compromised by pile-up in the MOS CCDs.

Figure 2.5-2. Interstellar absorption features in the MOS 1 spectrum of the Crab Nebula. Three fits are shown; the best fit with depleted oxygen and iron, the red curve assuming solar abundances and the green curve with the oxygen abundance set to zero.

2.5.2 The Crab-like Remnants G21.5-0.9 and 3C58

Of the ~225 known supernova remnants (SNRs) in our galaxy no more than 5% are classified as Crab-like remnants. The characteristic centre-filled radio and X-ray morphologies of the such SNRs is thought to be due to the presence of an active pulsar which powers a bright synchrotron nebula, although in many Crab-like systems there is no direct evidence for pulsed emission. A feature of the Crab-like remnants, which distinguishes them from both shell-like and composite-type SNRs (the latter typically exhibiting a filled-centre X-ray morphology within a radio shell), is the lack of any evidence for an outer shell structure marking the progress of the blastwave from the original supernova explosion.

G21.5-0.9 is a SNR with many of the characteristics of a Crab-like remnant. Recent X-ray observations made by Chandra have pinpointed the probable location of the pulsar within a very compact central core on a scale of ~2" embedded in a more extended (~30" radius) synchrotron nebula (Slane et al 2000, ApJ, 533, L29). XMM-Newton observations [157] reveal an extended ( r ~ 150") low-surface brightness X-ray halo in G21.5-0.9 (Figure 2.5-3). The near circular symmetry, the lack of any limb brightening and the non-thermal spectral form, all favour an interpretation of this outer halo as an extension of the central synchrotron nebula rather than as a shell formed by the supernova blast wave and ejecta. The X-ray spectrum of the nebula exhibits a marked spectral softening with radius, with the power-law spectral index varying from Gamma = 1.63 in the core to Gamma = 2.45 at the edge of the halo, remarkably similar to the spectral trend seen in the Crab Nebula.

3C58 is a beautiful example of a Crab-like filled-centre supernova remnant probably associated with the historical supernova of 1181 A.D. The high sensitivity and good spatial resolution of the EPIC cameras on XMM-Newton have been employed to search both for thermal emission from a central pulsar and for evidence of an outer thermal shell structure [25]. We place a stringent upper limit on thermal black-body emission from a putative neutron star at the centre of 3C58, a measurement which also rules out the "outer-gap'' model for emission from the polar caps of a pulsar unless the rotational energy loss is extremely low. Spectral analysis of the outer edge the 3C58 nebula shows that non-thermal processes are responsible for most of the emission but that a soft thermal component is required to fit the spectrum below 1 keV. If represented with an optically thin emission model, this component gives kT=0.2-0.3 keV. If it is associated to the Sedov expansion of the 3C58 shell, it is incompatible with the association between 3C58 and SN1181, unless there is strong deviation from electron-ion equipartition. However, if it is due to the expansion of the nebula into the inner core of moving ejecta, the X-ray spectra characteristics and the radio morphology of the outer nebula can be more easily reconciled (see Figure 2.5-4).

Figure 2.5-3. XMM-Newton EPIC MOS image of G21.5-0.9. The pixel size is 1'' and the image is 8' on a side. The image has been spatial filtered with a Gaussian smoothing mask with width sigma = 2 pixels. Logarithmic intensity scaling has been applied.

Figure 2.5-4. MOS 1+2 soft X-ray image of 3C58.The colour coded image and yellow contours refer to the X-ray data, whereas the white contours correspond to the lowest surface brightness features detected at 1446 MHz.

2.5.3 Cassiopeia A

An interesting feature in the high energy spectrum of the supernova remnant Cassiopeia A is a high-energy tail observed by both the Rossi X-ray Timing Explorer and the Compton Gamma Ray Observatory. The spectral form is described by a broken power law with break energy E_b=15.9 keV and photon index below the break of Gamma₁ = 1.8. Recent X-ray imaging observations, for example using BeppoSAX (Vink et al 1999, A&A, 344, 289), failed to determine the origin of this emission. However, the combination of large collecting area in the energy band 4.0 to 12.0 keV and an angular resolution of a few arc seconds afforded by the EPIC cameras on XMM-Newton have provided a unique opportunity to search for the origin of this hard tail [24].

Figures 2.5-5 and 2.5-6 show images of Cas A derived from the EPIC MOS cameras. The left-hand panel of Figure 2.5-5 shows the hard continuum above the energy of the Fe K emission. The distribution of flux in this hard band is very comparable to that in the softer continuum image shown in Figure 2.5-6. When we consider a spectral hardness ratio (right-hand panel of Figure 2.5-5), we do find significant changes over the remnant, however the bright features appear to have a very similar spectrum above 8.0 keV. XMM-Newton clearly detects the hard X-ray tail but the hard imaging and hardness ratio data indicate that this flux is not concentrated in the primary shock or within a few hard knots but is best described as a hard extension of the soft continuum emission from the whole remnant. The spectral form of the non-thermal high-energy tail is consistent with a simple SNR synchrotron emission model (e.g. Reynolds 1997, ApJ, 533, L29). However, in such a model the electrons are accelerated to extreme energies (TeV) at the primary shock and the associated synchrotron emission would be expected to be concentrated in the wound up magnetic field just inside the shock front. The hard continuum images from XMM-Newton indicate that the high-energy tail comes from both the bright X-ray knots and the bulk volume of the remnant. This favours an alternative suggestion due to Asvarov et al (1989, Sov. Ast, 33, 532) that the hard X-ray spectrum is dominated by non-thermal bremsstrahlung.

Detailed spectral fitting on a 15 x 15 grid of 20 arcsec pixels provides the abundance maps for Ne, Mg, Si, S, Ar, Ca, Fe and Ni. The abundance ratios are in good agreement with current models of explosive nucleosynthesis in the collapse of a 12 M₀ progenitor star [335]. The energy resolution, gain stability and gain uniformity of the EPIC MOS CCDs make it possible to detect emission line energy shifts of order 1 eV or greater providing sufficient counts are detected from the line and the line is not a blend of unresolved components. The Si K, S K and Fe K emission lines in the X-ray spectrum of Cas A are bright and well resolved by the MOS CCDs and provide an opportunity to map Doppler shifts over the face of the remnant with a spatial resolution of order 15 arc seconds. Initial results on the expansion rate are in agreement with previous Doppler and proper motion studies.

Figure 2.5-5. Continuum 8-12 keV (left) and hardness ratio (right) images of Cas A. The hardness ratio (10-12 keV)/(8-10 keV) is colour coded so that 0.1 is shown as black and 0.3 as white. The contour superimposed in green encompasses 37% of the total count in the 8-12 keV band; the remaining 63% of the hard flux is spread out over the rest of the remnant.

Figure 2.5-6. Continuum 4.0-6.0 keV (left) and Fe K equivalent width (right) images of Cas A. The right-hand panel is colour coded so that black corresponds to 0 keV and white to 4 keV and above.

2.6 Normal Star Forming Galaxies

M.J.Ward, J.P. Osborne, A. Burston, M. Goad, A. Hands, P. Lira, P.T. O'Brien, T. Roberts, R.S. Warwick, M.G. Watson, A. Zezas

2.6.1 XMM-Newton observations of M31: The Nearest Spiral Galaxy

The Andromeda Nebula (M31) is the nearest spiral galaxy to our own. Its relative proximity allows us to study the individual X-ray sources in a way that is impossible for our own Galaxy because of the large absorption in the Galactic plane and the wide distribution of Galactic sources over the sky with the added advantage that all M31 sources are at the same well established distance. XMM-Newton is well suited to the study of X-ray sources in M31 since a significant fraction of the whole galaxy can be covered in a single observation. In addition the possibility of day-long observations allows all sources with L_x ~ 2 x 10³⁴ erg/s to be detected, and the bulk of the period distribution of its low mass X-ray binaries to be covered. The large collecting area of the XMM mirrors also allows large numbers of counts to be collected from individual sources, allowing X-ray binaries in M31 to be studied in as much detail as has previously been possible for sources in our own Galaxy.

A large survey of M31 with XMM-Newton is now underway based on a total of 500 ks exposure time from the GT programme of the SSC and OM teams. Part of the scientific promise of these observations was discussed by Kolb, Osborne & Watson [209], who reviewed the importance of X-ray observations of high mass and low mass X-ray binaries in determining respectively the recent and historical star formation rates.

The XMM-Newton M31 survey has now started with two observations of the central 30' of the galaxy (Figure 2.6-1). Shirey et al [133] present a first analysis, demonstrating conclusively that the apparently diffuse emission really does come from diffuse gas (at a temperature of 0.35 keV), an important conclusion as M31 is often considered as a prototype early-type spiral galaxy. 116 point sources are also detected with luminosities in the range 6 x 10³⁵ - 4 x 10³⁸ erg s^-1, the luminosity function flattening below 2.5 x 10³⁷ erg s^-1 possibly due to differing formation and evolutionary histories of the different classes of X-ray binaries.

We have also made a first study of variability of the X-ray sources in M31 using observations of the core of M31 taken six months apart. Osborne et al. (2001, in press) identify 10 objects which have varied between the two XMM-Newton observations. Four of these objects are new. They include a bright X-ray transient which faded by at least a factor 4 from 10³⁷ erg s^-1 over the 6 month interval, fairly typical behaviour for an X-ray nova. Also detected was a long-lived transient, first seen by Chandra, and which was still within 25% of its discovery luminosity of a few 10³⁷ erg s^-1 after 14 months. Perhaps the most interesting discovery was of a "super-soft" source which was found to have 40% modulation at a period of 865 seconds (Figure 2.6-2) and which had faded by a factor of ten by the second XMM-Newton observation. This source has the shortest period of all known super-soft sources by a large margin, and points to a different modulation mechanism. One possibility is the spin modulation of a nuclear-burning, thermal-timescale accreting magnetic white dwarf, a type of object which has not previously been seen.

Figure 2.6-1. The core of M31 as observed by the XMM-Newton EPIC pn cameras in June 2000 (top) and December 2000 (bottom). A number of sources can be seen to have varied significantly, in particular the short period Super-Soft Source circled on the left and the X-ray nova circled above the centre.

Figure 2.6-2. The soft X-ray light curve of the new short period super-soft source XMM J004319+411758 (P=865 sec). This object may be the first of a new class of magnetic nuclear-burning accreting white dwarfs.

2.6.2 Chandra observations of the starburst galaxy M82

In many respects M82 is the archetypal starburst galaxy with its close proximity (3.6 Mpc), making it an ideal target for high spatial resolution studies. For this reason we have observed M82 on four separate occasions, using Chandra with either the High Resolution Camera (HRC) or the ACIS-I in the focal plane. Our results are presented in two papers, Kaaret et al [75] and Ward et al (2001, in press).

We find about 30 discrete X-ray sources, 12 of which are variable on a timescale of a few months, but with no evidence to date for periodicities. These unresolved sources are most probably either X-ray binaries or supernova remnants. We have examined the relative astrometry of the X-ray and radio sources in M82 to look for coincidences, and find four possible cases. These range in X-ray luminosity from ~3 x 10³⁷ erg s^-1 to a ~3 x 10³⁸ erg s^-1. Based on radio studies it is believed that these are likely to be young (< 100 yr) SNRs. The X-ray data do not have sufficient counts to give useful spectra (except for one case, see below), but their hardness ratios and the lack of variability are consistent with the SNR hypothesis.

Of the non-SNR X-ray sources, the most spectacular example is X41.4+60 [75]. which lies 9 arcsec (200 parsecs) from the kinematic centre of M82. This source increased in brightness by a factor 7, in the few months between two Chandra observations (Figure 2.6-3), and reached a luminosity of more than 10⁴¹ erg s^-1. The X-ray spectrum and high luminosity are both consistent with it being the same source as that observed previously by ASCA and claimed to be an AGN (Ptak & Griffiths 1999, ApJ, 517, 85), although the spatial resolution of ASCA was too low to show that it was not located at the nucleus. Since its discovery there has been very considerable speculation about the nature of this source. Intermediate black holes, of a few hundred solar masses have been much discussed. This assumes that the mass of the source corresponds to that calculated from the Eddington luminosity. An alternative, which reduces the mass of the compact object, involves the possibility of beaming (King et al 2001, in press). Another, less favoured, suggestion is that it is a young SNR expanding into a dense environment. While just consistent with the current data, the very large increase in flux is a problem for this model. On the other hand some support for the SNR scenario is provided by the exact spatial coincidence with a radio source which was first observed in the 1980's and which has subsequently faded by more than a factor of 10, and is now undetectable. In the future, X-ray spectroscopy will provide crucial information on the nature of this source. We have recently extended our X-ray studies of starbursts to include the most X-ray luminous example in the local universe, NGC3256. Lira et al [311] show that there are probably many examples of the ULS phenomenon in this galaxy, and in the future we will investigate quantitatively links between them and the starforming properties of their host galaxy.

Our work on M82 has lead to a fruitful collaboration with the theory group here at Leicester and has spawned a new area of observational investigation (see the section 2.6.4). Chandra observations are now opening up this area of study, because of their high spatial resolution, and previous studies based on ROSAT (e.g. [122]), suggest that ultra-luminous sources may be widespread.

Figure 2.6-3. Chandra observations of M82 obtained in October 1999 (left) and January 2000 (right) showing the central region of the galaxy. The variable ultra-luminous source is seen to the right of centre. An X-ray transient source (east of the ULS) has disappeared by the time of the second observation.

2.6.3 XMM-Newton observations of the starburst galaxy NGC 253

XMM-Newton observations have been used to study the extended X-ray emission and point-like source population of the famous southern starburst galaxy NGC 253 (Figure 2.6-4; [224]). A bright X-ray transient source was detected about 70 arcsec SSW of the nucleus. We also determine the spectrum and light curve of the brightest point source, and show that it is most likely a black hole X-ray binary. The unresolved emission of two disk regions can be modeled by two optically-thin thermal plasma components (with kT ~ 0.13 and 0.4 keV), whereas the nuclear spectrum implies the presence of three temperature regimes (kT ~ 0.6, 0.9 and 6 keV) with the higher temperature emission showing increasing absorption. The hottest component most likely originates from the starburst nucleus, since no non-thermal emission, indicative of an active nucleus, is required by the spectral modelling. Assuming that remnants of type IIa supernovae are responsible for the medium energy X-ray emission (above 4 keV), the presence in the EPIC data of the 6.7 keV emission line, allows us to estimate the supernova rate within the central region of the starburst to be 0.2 yr^-1. The EPIC and RGS data show that the X-ray plume in NGC 253 is limb brightened, and seen most prominently in the higher ionization lines. In contrast the lower ionization lines, below 0.5 keV, show the plume to be more homogeneously structured. Detailed multiple temperature modeling of the plume points to a mass-loaded out-flowing plasma close to the starburst nucleus.

Although NGC 253 and M82 are often discussed together as nearby examples of the starburst phenomemon, it is becoming increasingly clear from X-ray studies that there are significant differences between them (e.g presence of ULS in M82 and the relative contribution of the X-ray superwind). In our future work we will use larger samples (e.g. our Chandra Spiral Galaxy Survey) to determine the origins of these differences.

Figure 2.6-4. XMM-Newton EPIC image of NGC 253 showing the disk and nuclear regions. The red, green and blue colours correspond to three "ROSAT'" bands (0.2-0.5, 0.5-0.9 and 0.9-2.0 keV respectively). The hard 2-10 keV emission is shown as black/white contours.

2.6.4 The identification of an optical counterpart to the ultra-luminous X-ray source, NGC 5204 X-1

Though the presence of discrete, very luminous (L_x ~ 10³⁹ erg s^-1) X-ray sources in the outer regions of some nearby galaxies has long been known, the exact nature of these sources has remained a mystery. A small number are known to be associated with recent supernovae and are thought to be the result of the supernova exploding into a dense circumstellar medium. However, the majority of these "ultra-luminous sources" (ULS) are believed to be accretion-powered. Evidence for this comes both from the detection of short- and long-term X-ray variability in some examples of ULS (e.g. Ho II source, Zezas 1999 170), and from ASCA spectral studies which show that ULS often have multi-colour disc blackbody spectra consistent with emisson from an optically thick accretion disc around a black hole (Makishima et al 2000, ApJ, 535,632). The fact that some ULS undergo long-term spectral transitions between "hard'' and "soft'' states, similar to those exhibited by Galactic black hole candidates (e.g. Mizuno et al 2001, ApJ, 554, 1282) adds further weight to an accreting binary interpretation. However, much remains to be understood about such sources, in particular the nature of the accreting object - which, given the X-ray luminosity of such systems, could either have an intrinsic mass of 10² - 10⁴ M₀ (Colbert & Mushotzky 1999, ApJ, 519, 89) or be a lower mass object with beamed X-ray emission (King et al 2001).

We have initiated a programme of Chandra X-ray observations together with optical follow-up based on the WHT/INTEGRAL instrument, to investigate the nature and galactic environment of ULS. An early result of this work is the identification of a possible optical counterpart to the ultra-luminous X-ray source NGC 5204 X-1 [266]. Chandra data show that the X-ray source is point-like, with a luminosity of 5.2 x 10³⁹ erg s^-1 0.5 - 8 keV). It displays medium- and long-term X-ray variability in observations spanning a period of 20 years. The accurate Chandra position allows us to identify a blue optical continuum source (m_v = 19.7) at the position of NGC 5204 X-1 in our INTEGRAL data (Figure 2.6-5). Although we cannot completely rule out the possibility that we are observing a BL Lac object behind NGC 5204, the X-ray and optical source properties are consistent with the beamed X-ray emission of a high-mass X-ray binary in NGC 5204, composed of an O supergiant star with either a black hole or neutron star companion. It is also possible that the optical conterpart is comprised of multiple components and we plan to pursue this possibility by means of ground-based (AO) and HST observations.

Figure 2.6-5. A blue continuum reconstructed INTEGRAL image of the region containing NGC 5204 X-1, overlaid with the Chandra X-ray contours, clearly showing the optical counterpart to NGC 5204 X-1. The optical spectrum of the counterpart (right).

2.6.5 Do LINER 2 galaxies harbour low-luminosity active galactic nuclei?

The low-ionization nuclear emission-line region (LINER) phenomenon represents (potentially) the most common form of non-stellar nuclear activity in the local universe, occurring in 33% of galaxies and outnumbering low-luminosity Seyfert galaxies by 3:1. The presence of broad optical emission lines in the spectra of ~20% of LINERs demonstrates that bona fide low-luminosity active galactic nuclei (LLAGN) are present at least in a subset of objects (the so-called "type 1" LINERs). However, if broad emission lines are absent (in which case, by extension of the Seyfert paradigm, the source is categorised as a LINER 2), the presence of a LLAGN is far from certain, with collisional ionization by fast shocks and photoionization by either young, hot stars or planetary nebulae nuclei offering plausible explanations for the optical excitation.

X-ray observations provide a means whereby the presence of a LLAGN may potentially be distinguished from stellar processes. We have examined the ROSAT HRI spatial and ASCA spectral data for a homogeneous set of LINER 2 nuclei located in nearby, early-type spiral galaxies [268]. We find that the brightest X-ray source in each galaxy is positionally coincident with the galactic nucleus (Figure 2.6-6). When we exclude two sources, where there is good evidence that a LLAGN is present and dominating the X-ray emission, then for the remaining sources we find a remarkably similarity in the X-ray spectral form. Furthermore, the ratio of the flux in soft thermal emission compared to that in a hard non-thermal continuum has an average across the sample of 0.66+/-0.1, which is almost identical to that measured for the classical starburst galaxy NGC 253. As there is no obvious reason why the luminosity of the hard power-law continuum emanating from a putative LLAGN should be closely correlated with the thermal emission of the surrounding region, this suggests the X-ray emission from these LINER 2 galaxies is associated with the starburst phenomenon. Our results suggest that in many, perhaps the majority, of LINER 2 galaxies, the nuclear X-ray luminosity is not due to the presence of a LLAGN. The case for the presence of a LLAGN in all LINERs is therefore far from proven.

Figure 2.6-6. X-ray emission contour maps of two galaxies in the LINER 2 sample. The emission contours (in red) are superposed onto a 16 arcminute square Digitised Palomar Sky Survey negative image of each galaxy. Discrete X-ray source detections are indicated by a green cross.

2.6.6 XMM-Newton observations of Hickson Galaxy Group 16

Hickson-16 (or HCG-16) is a group of galaxies at z=0.0132, which is exceptional in having the highest concentration of starburst or AGN activity in the nearby Universe. The X-ray colour image obtained by EPIC (Figure 2.6-7) shows that all four of the major galaxies in HCG-16 are strong X-ray emitters [149]. In particular, NGC 833 possesses a very hard X-ray spectrum, consistent with the presence of a highly obscured active nucleus (N_H=10²³ cm^-2 and L_X=10⁴² erg s^-1). In fact the XMM-Newton spectra show that three out of the four bright HCG-16 galaxies contain obscured AGN (Figure 2.6-8). All of the galaxies exhibit spatially extended thermal X-ray emission associated with an active starburst component. In summary, the XMM-Newton observations demonstrate that both starburst and obscured type 2 AGN co-exist in members of this highly evolved system of merging/merged galaxies, implying a high probability for the formation of AGN as well as starbursts in post-merger galaxies. Of these four galaxies, only NGC 833 has an optical classification as a Seyfert. Our observations suggest that X-ray data can reveal the presence of a weak AGN even in cases where it co-exists with a starburst component.

Figure 2.6-7. Smoothed X-ray colour image of Hickson-16 made from EPIC MOS CCD data. In the image, red corresponds to < 800 eV and blue to > 3 keV. The very hard X-ray spectrum of the nucleus of NGC 833, which contains an obscured AGN, is readily apparent. Softer (cooler) diffuse emission from starbursts can be seen around all four bright galaxies.

Figure 2.6-8. X-ray spectra of the central regions of the two Hickson-16 galaxies, NGC 833 and NGC 835. Both spectra show a hard, highly absorbed power-law component, which is characteristic of an obscured AGN, in addition to a soft thermal component.

2.6.7 Ultra-luminous infrared galaxies revealed via infrared spectroscopy

The clear distinction between starburst activity and dust-enshrouded active galactic nuclei is observationally often very difficult to make (although see the previous section). Using UKIRT, we have obtained infrared spectroscopy in the H and K bands (1.5-2.4 microns), for a sample of ultra-luminous infrared galaxies (ULIRGs) Burston et al [294]. The main advantage of employing infrared over optical spectroscopy, is that it is far less affected by reddening caused by dust, which is ubiquitous in these objects. Amongst our sample we have found clear examples of obscured AGN, shown by the presence of broad (5,000 km/s, FWHM) Paschen and Brackett hydrogen recombination lines. In addition, there is strong evidence for the presence of an AGN inferred from the detection of the high ionization emission forbidden line of [SiVI], at 1.96 microns. This line cannot be produced solely by hot stars, and hence even in the absence of broad recombination lines due presumably to the large amounts of extinction, the detection of [SiVI] is a strong indication that an AGN is present.

Some ULIRGs lack both broad lines and [SiVI], but nevertheless exhibit strong molecular hydrogen emission. We have used several H2 line ratios, and compared these with state-of-the-art models, in order to determine the excitation mechanism. Although the results are not totally clear cut, it appears that in several cases there is a link between the level of interaction of the galaxy, and the dominance of thermal excitation, as would be expected if shocks are propagating within the molecular gas. X-ray observations may also provide very useful diagnostics of shocks and we are currently analysing recent Chandra observations of ULIRGs e.g. NGC 6240 (Lira et al 2002, in press).

2.7 Active Galactic Nuclei

P.T. O’Brien, J. Reeves, S. Goad, G. Griffiths, D. Law-Green, C.G. Page, K.A. Pounds, T. Roberts, S. Sembay, M.J.L. Turner, S. Vaughan, M.J. Ward, R.S. Warwick

2.7.1 Iron Kalpha emission in the Seyfert 1 Galaxies Mrk 205 and Mrk 509

Markarian 205 and Markarian 509 are bright, high luminosity (L_X > 10⁴⁴ erg s^-1), broad-lined Seyfert 1 galaxies. Both these sources were observed early on in the XMM-Newton mission. In the case of Mrk 205, the EPIC CCD spectra revealed a complex Fe Kalpha emission line profile [121] consisting of a neutral, unresolved fluorescent line as well as a broad (FWHM 30,000 km s^-1) component centred at 6.7 keV (Figure 2.7-1). As the velocity width of the 6.4 keV line is narrow (~ 3000 km s^-1), it must originate from matter distant from the Active Galactic Nucleus (AGN). Indeed it appears likely that the narrow line is due to X-rays reflecting off a “molecular torus”, thought to be the medium that obscures the central engines of Seyfert 2 galaxies in the context of Seyfert Type-1/Type-2 unification schemes. In contrast, the high velocity width of the 6.7 keV line implies that it is emitted from the accretion disc, close to the central supermassive black hole.

The XMM-Newton observations of Mrk 509 have revealed a very similar iron-line profile [319]. Again there are two distinct components, a narrow, fluorescent line at 6.4 keV and a broad line centred near 6.7 keV. Modelling of the line profiles in both AGN using accretion disc models provided by Sergei Nayakshin, indicates that the broad 6.7 keV line results from predominantly He-like iron in the highly photoionized skin of the inner accretion disc. The high level of ionization, particularly in Mrk 509, implies that the source of the illuminating hard X-rays are highly concentrated in intense magnetic flares, located directly above the inner disc surface. The accretion disc models do not explain the narrow, cold fluorescent line at 6.4 keV. XMM-Newton and Chandra observations are showing that the 6.4 keV line appears to be a generic feature of low to moderate luminosity AGN. At high luminosity (e.g. PKS 0558-504, [103]), no such narrow line is detected (EW < 10 eV). This trend is consistent with dusty, magnetised wind models in which the solid angle subtended by the molecular torus, as seen from the central engine, decreases with luminosity due to the field lines being forced down towards the disc plane by radiation pressure.

Figure 2.7-1. The iron K line profile of Mrk 205. In addition to a powerlaw-like continuum, the 'best-fit' model consists of both a broad 'ionized' line at 6.7 keV and a narrow 'cold' line at 6.4 keV.

2.7.2 A Comptonised accretion disc in the narrow-line quasar, PKS 0558-504

PKS 0558-504 is a luminous AGN (z=0.137, L_x = 4x10⁴⁵ erg s^-1), which although often classified as a narrow-line Seyfert 1 galaxy, actually has a bolometric luminosity in the quasar range. The XMM-Newton observations of PKS 0558-504 [103] show a large excess of soft X-ray emission below ~3 keV (Figure 2.7-2). Strong soft excesses are common in NLS1s (e.g. [155]). The generic explanation is that these objects have accretion rates close to the Eddington rate. The soft X-ray excess in PKS 0558-504 can be modelled by a multi-temperature disc blackbody spectrum extending from the optical/UV/EUV (the “big blue bump”) into the soft X-ray range. However, to reproduce the observed spectral shape, the disc emission must be Comptonised via a hot (~4 keV) layer of electrons located at or above the disc surface.

Figure 2.7-2. The broad-band X-ray spectrum of PKS 0558-504, showing a substantial soft X-ray excess emitted below 3 keV. Here the soft excess has been modelled with a multi-temperature blackbody with characteristic temperatures (kT) of 75 eV, 170 eV and 450 eV.

2.7.3 The detection of an iron-K line in a high-redshift object

XMM-Newton has the collecting area to facilitate detailed study of high-redshift AGN for the first time. PKS 0537-286 is an extremely high luminosity (L_x > 2x10⁴⁷ erg s^-1), high redshift (z=3.104) radio-loud quasar observed early in the mission. The EPIC spectra [120] reveal an X-ray continuum apparently dominated by the hard inverse Compton component associated with a relativistic jet orientated at an angle close to the line-of-sight. The observations also show a weak iron-K line observed near 1.5 keV, corresponding to 6.15 keV in the quasar rest-frame. To date, this is the highest redshift iron Kalpha line observed in an AGN (Figure 2.7-3). The rest-energy of the line (6.15 keV) implies an intrinsic velocity shift (of (delta)v = 15,000 km s^-1) associated with the quasar, which could be caused by gravitational redshift or result from inflow onto the quasar nucleus.

Figure 2.7-3. The observed iron-K line in the bright, high redshift quasar PKS 0537-286. The line is at 6.15 keV in the quasar rest-frame, but is redshifted to an observed energy of 1.5 keV.

2.7.4 ISO observations of quasars at z~1

Nearby luminous AGN show a distinct "bump" in their mid-infrared spectra centered around 3 microns, thought to be due to re-radiation of the central quasar continuum by heated dust at the inner edge of an obscuring torus. It is not currently known whether the dusty torus is still present in more luminous objects.

We have conducted mid-infrared photometry of 13 optically-selected, highly luminous QSOs at z~1 with the ISOPHOT-S spectrometer and the ISOCAM CVF imaging spectrophotometer to look for the 3 micron "dust bump". Secure detections were made in 3 objects [308]. For the remaining 10 objects, we can set 3sigma upper limits. We use these data to estimate limits on the sublimating dust mass in medium-redshift quasars. We find that the non-thermal contribution to the mid-infrared flux in non-blazar QSO's is negligible over the range of luminosities and redshifts studied. The observed turnover in dust mass at intermediate redshifts/luminosities is explained either as a shift between two distinct populations of quasars (primordial and short-lived nearby merger objects) or as a density cutoff in the dust distribution. We estimate the density cutoff to occur at r~4 pc, and suggest that this represents the location of the emitting material, which could be associated with a dusty, molecular torus.

2.7.5 The Big Blue Bump and X-ray emission in Seyfert 1 galaxies

The most prominent feature in the broad-band spectra of many AGN is the 'big blue bump' (BBB), which contains a large fraction of the bolometric luminosity. The soft X-ray excesses seen in many AGN may be the high-energy tail of the BBB, but the exact relation between the optical/UV and X-ray emission is still unclear. In addition to detailed spectroscopic studies, we have investigated this relationship via extensive, multi-wavelength monitoring campaigns. Two objects have been studied in great detail, namely NGC 3516 and NGC 7469.

NGC 3516 was monitored simultaneously with HST, RXTE and ASCA for 3 days, the most intensive such campaign yet undertaken [47]. The X-ray fluxes were strongly variable (Figure 2.7-4) with the soft (0.5-2 keV) X-rays showing stronger variations (~65% peak-to-peak) than the hard (2-10 keV) X-rays (~50% peak-to-peak). In striking contrast, the optical continuum showed much smaller but still highly significant variations: a slow ~2.5% rise followed by a faster ~3.5% decline.

The soft and hard X-ray variability in NGC 3516 was strongly correlated with no lag (3sigma upper limit < 0.07 d). The optical continuum also varied with no lag within the band (3sigma < 0.15 d), but was not correlated with the X-ray flux. These results are inconsistent with reprocessing models in which the X-ray source heats a stratified accretion disc which then re-emits in the optical/UV.

In contrast, a ~30 d, near-continuous observation of the Seyfert 1 galaxy NGC 7469 reveals that the X-ray spectral index is correlated with the UV flux and the broad-band X-ray photon flux is also correlated with the UV continuum. This is consistent with thermal Comptonisation models in which the UV provides the seed photons for the X-ray emission. In this model, absorption and reprocessing of EUV/soft X-rays in a standard accretion disc produces a variable seed photon distribution which is up-scattered into the X-ray band.

Figure 2.7-4. X-ray, ultraviolet and optical continuum light curves of NGC 3516. The light curves are, from the top, the ASCA hard (2-10 keV) band, the RXTE hard (2-10 keV) band, the ASCA soft (0.5-2 keV) band, the HST ultraviolet (1360 Å) band, and the HST mean optical band.

2.7.6 Long-term variability of AGN broad emission-lines

While broad emission-line flux variations can yield information concerning the spatial distribution of the line emitting gas, profile shape variations can yield important clues as to the nature of the fuelling process in general. To this end five Seyfert 1 galaxies were observed with WHT/ISIS in both Halpha and Hbeta from Dec 1997-Feb 2001 at 6 separate epochs. Since the same targets had been intensively monitored by the LAG international collaboration over a 6 month period in 1990, this provided information on both the short and long-term variability properties.

After the removal of contaminating narrow emission-lines, and in the far-optical, FeII, we can confirm profile shape variations in all 5 targets (Goad, O'Brien, Robinson 2001 in press). The variations are generally asymmetric about line centre, are larger in the core than in the wings and, in at least one object, show evidence for a double-peaked structure, possibly the signature of a disc-like structure for the line-emitting gas (Figure 2.7-5). Comparison of the new data with that from the 1990 LAG monitoring campaign suggests that the BLR retains a memory of the environment in which it sits. Thus, the spatial distribution and kinematics of the optical line-emitting gas appear to be largely dominated by the central super-massive black hole.

Figure 2.7-5. The monitoring data for NGC 4593. Upper panel: the mean (solid line) and rms (dashed line) profile formed from scaling to the forbidden [SII] doublet. Middle Panel: the mean deviation profile delta(v), essentially the average of the moduli of the difference spectra. Lower panel: the mean deviation of the residual profiles phi(v), found after subtracting the average profile scaled by the corresponding integrated flux. phi(v) emphasizes changes in profile shape.

2.7.7 A Seyfert galaxy sample selected at 1/4 keV

Seyfert-type galaxies with unusually steep X-ray spectra can very often be classed optically as Narrow-line Seyfert 1s (NLS1s). This class of objects is gaining increasing attention as a result of their extreme properties including their ultrasoft X-ray spectra. However, until recently there has been no complete sample of X-ray selected NLS1s available for detailed study. We have used the ROSAT Bright Source Catalogue to extract a complete sample of sources selected in the energy band 0.1-0.4 keV (Vaughan et al 2001, in press). Subsequently we have carried out a programme of ground-based optical spectroscopy (see Figure 2.7-6) which has lead to the complete optical identification and categorisation of this set of sources. Our 1/4 keV-selected sample is comprised of 54 Seyfert galaxies, 20 BL Lacertae objects, 4 clusters and 27 Galactic stars or binaries. Remarkably 40% of the Seyferts can be classified as NLS1s.

Correlation analysis has confirmed the well-known relations between X-ray and optical spectral properties such as OIII/Hn ratio, optical FeII strength and Hbeta width. The various inter-correlations are most likely driven by the shape of the photoionizing continuum. We argue that a steep X-ray spectrum is a better indicator of an extreme set of physical properties than is the narrowness of the optical Hbeta line. For example, our analysis confirms that optically defined NLS1s do not show enhanced optical FeII emission, compared to other Seyfert 1, as has been previously suggested. It is the ultrasoft Seyferts (defined on the basis of their X-ray properties) that tend to show stronger FeII emission. Our 1/4 keV sample thus represents the ideal one in which to search for extremes of behaviour.

Correlation studies were also used to isolate a number of Seyfert galaxies with apparently "anomalous" properties. Of particular interest are the six objects with relatively weak permitted line emission (Hbeta and FeII) and weak optical continua. Such objects are rare in soft X-ray surveys, but two of these (IC 3599 and NGC 5905) are known to be transient AGN in which the X-ray flux has faded by a factor ~100. If the other four objects also turn out to be transient, this would demonstrate that 1/4 keV surveys provide an efficient way of finding this interesting class of object.

Figure 2.7-6. Close-ups of the optical spectra around Hbeta-OIII for three 1/4 keV Seyferts, showing the range of optical properties. In each panel the topmost curve shows the original spectrum, the middle curve shows the spectrum after FeII subtraction and the lower curve shows the model FeII emission.

2.7.8 X-ray spectral variability in BL Lac objects

BL Lac objects are a sub-class of blazars; sources whose broad-band continuum emission is dominated by relatively featureless non-thermal radiation. The rapid flux variability exhibited by blazars is generally assumed to be the result of the rapid motion of emission components contained within a relativistic jet. Jet models fall into two main categories: the inhomogeneous model and the homogeneous model. In the former the jet is assumed to be a cylindrically symmetric structure with the cross-section, particle density and magnetic field strength varying with the radial distance. Injected electrons cool both by synchrotron radiation and adiabatic expansion of the jet. In the latter, however, the particle distribution and magnetic field are assumed to be homogeneous throughout the emission region. In these models electrons must escape from the region on a timescale shorter than the synchrotron loss timescale and then stop radiating otherwise the predicted spectral slope in the radio would be much steeper than observed. Studying the variability behaviour of both the spectrum and flux of BL LACs provides one method of constraining jet models. The relationship of the variations within different energy bands can, in principle, help to constrain the geometry of the emission region on the macroscopic scale and identify the physical radiation and loss processes on the microscopic scale.

XMM-Newton has recently observed a number of BL Lac objects as part of the PV-CAL program, since their smooth X-ray spectra often prove useful tests of the instrument calibration. Aside from its high throughput, a key advantage of XMM-Newton for spectral variability investigations is the 48-hour orbit which allows long continuous observations. Recently Edelson et al [261] have studied light curves from two such observations of PKS 2155-304 (Figure 2.7-7). A cross-correlation analysis shows that there is no evidence for inter-band lags to a limit of Tau <= 0.3 hrs. The lack of an interband lag suggests that the light-crossing time is longer than the cooling time and that any intrinsic changes in the slope of the electron distribution is smeared out by light travel-time effects. The data also imply that Bgamma^1/3 > 2.5 G.

Figure 2.7-7. The XMM-Newton EPIC light-curves of PKS 2155-304 for two observing periods. From top to bottom the light curves correspond to MOS (0.1-12 keV), PN (0.1-12 keV) and then four PN subands 2-12 keV, 0.9-1.7 keV, 0.4-0.75 keV and 0.2-0.35 keV.

2.8 Clusters of Galaxies

G.C. Stewart, S. Dos Santos, A Pappa, L Spurgeon, M.G. Watson

2.8.1 The surface brightness profiles of clusters and groups

While XMM-Newton has much improved sensitivity and spectral resolution compared to ROSAT, the latter still has the advantage of a very large database of pointed observations of clusters and groups. Moreover, the reduction of ROSAT spatial data, including vignetting and PSF effects, is now well understood. Thus, the study of the statistical properties of large samples of objects is well served by archival ROSAT data. In particular, the relative insensitivity of the PSPC to temperature variations means that the surface brightness profiles (hereafter SBP) of clusters and groups give direct access to the gas density profile. It has been shown that these profiles, beyond the central region (where cooling is important due to the high densities), are generally self-similar in shape (e.g. Neumann & Arnaud 1999, A&A, 348, 711; Mohr, Mathiesen & Evrard 1999, ApJ, 517, 627). Nevertheless, there are two main problems with previous analyses. Firstly, analytic models are fit to the surface brightness profiles (SBP), a procedure which, in some circumstances, can introduce spurious correlations between the parameters of the model. This in turn can add to the scatter and possibly obscure real underlying physical correlations. Secondly, the earlier analyses concentrate on clusters with T > 3 keV and do not assess the variation of parameters over the full range of the halo mass. Indeed, while one study showed that the density profile is shallower in groups (Ponman, Cannon & Navarro 1999, Nature, 397, 135), these results were not subsequently confirmed.

We have begun a study of the SBP of clusters and groups. We have reduced the PSPC pointed data of 22 clusters and 15 groups and extracted a median SBP. Instead of fitting this SBP with an analytic model, we are using a Principal Component Analysis (PCA) to extract meaningful information, thus avoiding any intrinsic correlation induced by the fit. Comparing the principal components derived from observational data with simulated values, one can infer how the SBPs change with the underlying mass of the system. Preliminary results of this approach using data from 17 of the clusters are promising (Figure 2.8-1). We find 2-3 components are required and sufficient to explain the SBPs of both groups and clusters. The cluster SBPs are well represented by a single large scale component with a slope of ~2-2.5 with a core component of fixed radius in units of the virial radius (Spurgeon et al in preparation).

Figure 2.8-1. The results of the PCA analysis. The 3 principle components contributing 85%, 10% and 3% of the total variance in the sample are shown in the right panel while in the left the reconstructed profiles for three subsamples are shown and compared to a standard beta = 2/3 profile.

2.8.2 XMM-Newton Observations of cooling flow clusters

The number of cluster datasets available from XMM-Newton has to date been limited but the quality of the XMM-Newton data and its ability to impact on our understanding of the physical conditions in the hot intra-cluster medium (ICM) is already apparent. Despite limitations in both the calibration and background subtraction techniques for extended sources currently available in the XMM SAS, relatively robust conclusions are already available. Key topics to-date have been the spectroscopy of the central regions of cooling flow clusters, accurate temperature profiles to large radii (almost the virial radius in some cases) and detailed abundance gradient analysis.

The data from 2 bright nearby clusters with previously known cooling flows have been analyzed using standard annular spectroscopy [26, 143]. The radial temperature profiles found using a single component thermal plasma model for A1795 are shown in Figure 2.8-2. Clear decreasing temperature profiles are found in the central regions associated with the cooling flow. The heavy element abundances also show evidence for strong central concentration. The XMM-Newton data resolves both the temperature structure and abundance gradient at significantly higher spatial resolution and with greater precision than previously obtained with ASCA. The results are in agreement with those previous studies. The higher precision and greater spatial resolution do however allow a more detailed analysis of the gas properties within the cooling flow and this is aided by high resolution spectroscopy of the central regions using the RGS. The surprising result is that there is little or no evidence for the emission expected from gas cooler than some 'floor' temperature which appears to be a function of the cluster mass. For A1795 the minimum temperature component allowed is ~1.5 keV, while for M87 it is ~0.6 keV. A number of plausible explanations have been proposed and these are currently under detailed investigation.

Figure 2.8-2. The variation of temperature, density, abundance and absorption column as a function of radius in A1795.

2.8.3 Serendipitous clusters discovered by XMM-Newton

The galactic supernova remnant G21.0+0.9 is one of the calibration/PV targets of of XMM-Newton. The EPIC images revealed a bright extended (~2 arcmin) X-ray source some 15 arcmin away from the SNR [265]. The spectrum of the source is well fit with a thermal bremsstrahlung model, with a particularly strong iron feature at a redshift of 0.12. The obvious conclusion is that this a cluster of galaxies serendipitously detected close to the Galactic plane. Soft X-ray absorption corresponding to a column density of ~8 x 10²² cm^-2 causes the spectrum to be cut-off below ~2 keV (Figure 2.8-3). This column, which is equivalent to an optical extinction A_V ~ 10, is consistent with the non-detection of galaxy clusters in deep images of the region. The cluster has a temperature and luminosity of ~6 keV and 4 x 10⁴⁴ erg s^-1, consistent with the locally derived temperature-luminosity relation; the inferred cluster mass is a few x 10¹⁴ M_o. There is evidence for a cooling flow with a mass flow rate of ~300-600 M_o yr^-1.

This work demonstrates that XMM-Newton is capable of detecting clusters in regions of the sky previously barred from study, thus, in principle allowing a more complete determination of the local mass distribution.

Figure 2.8-3. The XMM EPIC spectrum of the serendipitous cluster clearly showing the strong redshifted iron line and high absorption.

2.8.4 Modelling the temperature profile of clusters of galaxies

Over the last two years we have studied the temperature profiles of clusters and modeled (via analytic and semi-analytic models) the gas equilibrium in the potential well of these systems. Recently we have built a new model of gas hydrostatic equilibrium in clusters, where the temperature profile (hereafter TP) is structured by local electronic thermal conduction [260]. We are just beginning the comparison of this TP with observational data from XMM-Newton.

While conduction is certainly suppressed in the central parts of clusters and during mergers, little is known of its properties outside the cooling-flow radius. Our model allows a physically motivated analytic expression for the TP to be derived, which compares very well with observations and numerical simulations of clusters. Moreover, using the observed surface brightness profiles of clusters, we can predict the polytropic index and the gas fraction profiles. These compare very well with spectroscopically resolved X-ray data. The model provides the basis for a new flavour of semi-analytic model (see below).

2.8.5 Unifying groups and clusters in a single model

We have designed a new semi-analytic model, in collaboration with J. Devriendt (Oxford University) and O. Doré (IAP, France) which uses the above-cited conduction-structured TP and numerical simulations for the dark matter component of clusters and groups (performed at IAP). A shock model at the virial radius, together with entropic constraints at the centre allow the prediction of the temperature profile without any assumption of isothermality or an unphysical polytropic link between temperature and density. The evolution of the central entropy is governed by the entropy evolution of the IGM in the universe obtained from an independently validated model (Valageas & Silk 1999, A&A, 350, 725) in two different cases: in the first one, the re-heating is provided by SNe explosions only, while in the second one, AGN and quasar activity provide the entropy injection. Both cases were tested against a number of observations, including the L_X-T relation, the change in surface brightness profiles from clusters to groups, the baryon fraction in these systems and the entropy floor. The use of the entropy evolution model does not allow any renormalisation and the shape and normalization agreement with several observed correlations are impressive. The agreement of the results with the local clusters and groups will allow us to predict the evolution of several correlations with red-shift, which will be compared with XMM-Newton and Chandra data. The model is also to be used to test the procedures for removing the cluster Sunyaez-Zeldovich (SZ) foregrounds in the all-sky CMB Planck mission (IAP) (Dos Santos 2001, in preparation).

For the first time, to our knowledge, we have linked groups and clusters of galaxies in a unique analytic model. Taking into account the competition between shocks and an observed entropy floor, we have found a simple analytic expression for the entropy jump in the shock model first described by Cavaliere et al (1998, ApJ, 501, 493). This expression fits the data of Ponman et al very well. After rewriting the X-ray luminosity and the SZ decrement in terms of entropy, this allows us to express analytically the L_X-T and y-T relations, including the observed bending in the groups mass range. The normalization of these relations is also predicted and compares very well to the data, using only the observed entropy floor value. This analytic model sheds light on the specific entropy profile formation in clusters and groups, and allows the redshift evolution of the L_X-T and y-T relations to constrain directly the entropy evolution of the intergalactic medium, and thus the re-heating history of the universe. Moreover, combined with a mass function for structures (e.g. the so-called Press & Schechter approximation), it allows analytic predictions to be made for future group X-ray and SZ observations (Figure 2.8-4) (Dos Santos & Dore 2001, submitted).

Figure 2.8-4. Left panel: Predictions for the Lx-T relationship for models with no (solid line), supernovae (dashed) and QSO (dotted) pre-heating compared to observations. Right panel: The specific entropy from different pre-heating models as a function of temperature (mass) compared to observations

2.9 X-ray Surveys

M.G.Watson, P.T. O’Brien, G.C. Stewart, M.J. Ward, R.S. Warwick

2.9.1 Surveys carried out with ROSAT and ASCA

Our collaboration with groups in Durham, Greece, Australia and the US on X-ray data from ASCA and ROSAT observations of the Durham UVX quasar sample fields, has continued. A number of important new results have emerged. Highlights include:

• The average variability of QSOs as a function of redshift and Luminosity

  Using a flux limited ROSAT sample of QSOs, Almaini et al [1] found relationships between the ensemble average variability of QSOs and their luminosity. At low redshifts the amplitude, on timescales of 10,000s, decreases with luminosity. This is consistent with the luminosity and size of the X-ray emitting region scaling with the mass of the central black hole. At redshifts >0.5, however, this trend no longer exists with the variability, if anything, increasing with luminosity (see Figure 2.9-1).

• The average QSO X-ray spectrum and its cosmic evolution

  While the vast majority of the large sample of QSOs detected in our survey are too faint for individual spectral parameters to be determined it has been possible to investigate the integrated spectra of QSOs in different redshift bands [23]. There is clear evidence that the spectrum over the ROSAT band hardens with redshift. The best empirical fit to the data suggests that this hardening is due to a reduction in the importance of a soft component in the spectrum and that the underlying power-law component maintains a constant slope consistent with that found for local bright AGN.

• A rare example of an obscured high-z QSO

  While the generally accepted model for the production of the X-ray background is that it is the integrated emission from a AGN including many with a range of (high) intrinsic absorptions, very few examples of the absorbed type II population have been found at high redshift. In Georgantopoulos et al [53] we reported on the detection with both ROSAT and ASCA of a broad-line example at a redshift of 2.53. The X-ray spectrum of this object is consistent with the canonical local AGN power-law and an absorption column of ~10²³ cm^-2 in line with expectations of the background synthesis model, although an alternative model with a flat power-law and no intrinsic absorption cannot be ruled out. The inferred optical obscuration, from the detection of broad Halpha and the its broad-band colours, is low (A_v ~ 3).

• The broad-band spectra of faint QSOs

  From our fields 21 QSOs have been detected over the 0.1-10 keV band with ROSAT and ASCA with sufficient signal-to-noise to investigate the variation of their individual spectral properties through hardness ratios and their integrated broad-band spectrum . The QSOs show a broad range of hardness ratios with a tendency to become harder at lower fluxes (Figure 2.9-2). The hardest sources either have very flat intrinsic spectra or require substantial intrinsic absorption. The integrated spectrum is flatter than the canonical AGN spectrum at Gamma ~ 1.5, close to the X-ray background slope.

Figure 2.9-1. Left: mean variability amplitude as a function of luminosity for low-redshift QSOs; Right: the corresponding figure for high redshift (z>0.5)

Figure 2.9-2. The hardness ratio (0.5-2.0 keV/2.0-10. keV) as a function of flux for ROSAT/ASCA deep survey QSOs. The horizontal lines indicate the predicted hardness ratio for different spectral forms (an unabsorbed power-law or a Gamma=1.9 absorbed power-law).

2.9.2 Studying the Lockman Hole with XMM-Newton

The Lockman Hole, one of the best studied sky areas over a very wide range of wavelengths, was the subject of the first deep X-ray survey made with XMM-Newton observatory during its performance verification phase, with a total exposure of ~100 ksec. The initial results of this study appear in Hasinger et al [66]. The combined EPIC data from the Lockman Hole observation provided sensitivity limits of 0.31, 1.4 and 2.4 x 10^-15 erg cm^-2 s^-1 in the 0.5-2, 2-10, and 5-10 keV bands respectively. Within an off-axis angle of 10 arcmin total source detections of 148, 112 and 61 sources were made in each band respectively. Comparison of the logN-logS relationships in the three bands shows good accord with previous results. In the 5-10 keV band these observations present the deepest X-ray survey ever, about a factor 20 more sensitive than the previous BeppoSAX observations. With the help of X-ray spectral diagnostics and earlier ROSAT results, a large fraction of the new sources could be classified. XMM-Newton detects a significant number (~40%) of X-ray sources with hard, probably intrinsically absorbed X-ray spectra, confirming a prediction of the population synthesis models for the X-ray background.

2.9.3 The XMM Survey Science Centre “XID” programme

The high throughput, large field of view and good imaging capabilities of XMM-Newton mean that it detects significant numbers of serendipitous X-ray sources in each pointing, e.g. see Figure 2.9-3. A typical XMM-Newton observation reaches fluxes of ~10^-15 erg cm^-2 s^-1 in the 0.5-2 keV band and ~10^-14 erg cm^-2 s^-1 in the 2-10 keV band. The accumulating serendipitous data from on-going XMM-Newton observations thus constitutes a deep, large area sky survey, representing a major resource for a wide range of programmes.

The scientific themes addressable via the serendipitous XMM sky survey include:

• The importance of obscuration in faint AGN populations

• The evolution of the quasar luminosity function with redshift

• The nature of faint X-ray galaxies and their contribution to the X-ray background

• The evolution and luminosity function of clusters of galaxies and the nature of density fluctuations in the early Universe

• The coronal activity in stars and its dependence on luminosity, spectral type, stellar rotation and age

• The space density of accreting binary systems

The Core Programme aims to obtain identifications for a well-defined sample of X-ray sources drawn from selected XMM-Newton fields, primarily using optical/IR imaging and spectroscopy. The principal objective is to obtain a completely identified sample which can be used to characterise the XMM source population sufficiently well that this knowledge can be used to assign a 'statistical' identification to a large fraction of all the sources in the XMM serendipitous source catalogue.

The Core Programme approach involves two samples: one drawn from the high and one from the low Galactic latitude sky. The high Galactic latitude sample consists of three subsamples, each containing ~1000 X-ray sources in three broad flux ranges: f_x > 10^-15 ; f_x > 10^-14 ; f_x > 10^-13 erg cm^-2 s^-1 in the 0.5-4.5 keV band. The size of the subsamples is dictated by the need to identify enough objects to reveal minority populations. Studying sources at a range of X-ray fluxes is necessary because we already know that the importance of different source populations changes with X-ray flux level.

The current emphasis in the SSC XID programme is on the medium and bright flux high latitude samples, and the low Galactic latitude sample, which are well-matched to the available ground-based observing facilities.

The XID Imaging Programme aims to obtain optical/IR photometry and colours for a large number of XMM-Newton fields. The programme rationale is based on the fact that a combination of X-ray flux, X-ray colours, optical magnitude and optical colours will provide the key parameters which make possible an accurate 'statistical' identification of the XMM sources. This is possible using the results from the Core Programme which characterise the X-ray source populations, thus providing the link, in a statistical sense, between the source identification and these basic parameters. Multi-colour optical imaging provides good discrimination between object types (e.g. AGN-star separation) as well as photometric redshifts, whilst IR imaging has an important role to play since the counterparts to obscured X-ray sources are also expected to show significant optical reddening.

Leicester has a central role in the planning, implementation and coordination of the XID Programme, with particular emphasis on the provision of reliable X-ray source lists from XMM-Newton observations and in establishing the astrometric accuracy of the detections.

Figure 2.9-3. EPIC images of Mkn 205. Left: soft band (0.5-2 keV) images; right: the corresponding hard band (2-10 keV) image.

2.9.4 Early XID programme results

The SSC XID Programme started in April 2000. As noted above the current emphasis of the programme is on the high latitude medium and bright flux samples, and the low latitude sample. A substantial amount of the observing time for the current programme was awarded to the XID Programme in both 2000 and 2001 within the Canary Islands International Time Programme (ITP; under the auspices of the “AXIS” project). The ITP awards bring 5% of all the telescopes on the Canaries, in particular the WHT, INT, TNG and NOT. Substantial additional telescope time has been gained on other telescopes, notably CFHT, ESO-MPG 2.2m as well as on Magellan 6m and the Subaru 8.3m.

To date deep optical and/or IR multi-colour imaging has been completed on more than 70 XMM-Newton fields, whilst spectroscopic identifications have been established for ~200 high-latitude sources and ~50 low latitude sources.

Figure 2.9-4 shows the finding charts and optical spectra of three example identifications made in the early part of this programme, which give a flavour of what has been achieved to date.

It is premature to discuss the results in any detail at this stage, as the programme is only just starting to accumulate statistically useful samples of identifications, we can nevertheless make some general remarks. In the high galactic latitude fields for which we have spectroscopic data so far 65% of the identifications are 'type 1' broad-line unabsorbed AGN, consistent with expectations from current models of the XRB. The remainder of the identifications include NELGs (20%) & galaxies (6%). The redshift distribution of the identified sources peaks at z ~ 1-2, in line with expectations for this sample. Of note is the identification of 2 definite and 1 possible broad absorption line (BAL) QSOs (see Figure 2.9-4), more or less doubling the number known from previous X-ray survey work and clearly demonstrating the importance of the increased sensitivity of XMM-Newton, especially at higher photon energies.

At low latitudes active stars dominate the identifications, as expected, but the programme has already turned up one new Be-star X-ray binary system. Further spectroscopy of faint low-latitude candidates will be taking place in the next few months. Many of the low-latitude fields under study have been imaged in Halpha as well as broad-band filters. This is a powerful approach which allows the isolation of Halpha excess candidates (e.g. CVs, some X-ray binaries) for follow-up spectroscopy, as is illustrated in Figure 2.9-5.

Figure 2.9-4. Optical spectra and finding charts of the counterparts for three serendipitous XMM-Newton sources. Left panels: an object in the Mkn 205 field identified with a z=0.33 galaxy. Centre panels: an object in a GT field identified with a BAL quasar at z=1.82. Right Panels: an object in the same field identified with a quasar at z=2.26.

Figure 2.9-5. Halpha-r vs. r colour magnitude diagram for objects detected in INT WFC images of a low-latitude XMM field. Background greyscale image represents the density of field object detections. Overlaid red dots are potential candidates within 5 arcsec of the X-ray centroid, green dots are potential candidates within 5 < r < 8 arcsec.

PUBLIC UNDERSTANDING OF SCIENCE

Figure 3-1. Aerial view of the National Space Centre, Leicester (courtesy of NSC)

This increased profile has attracted a number of additional activities, enhancing further our position as a centre of excellence in space science and astronomy and increasing our role in the PUS/Education arena. In July 2000, the department hosted the International Physics Olympiad. Members of XRA took the key roles in this activity, leading to a highly successful event. We were able to generate a number of undergraduate scholarships from the sponsors which will fund overseas students to study in our Department. The organising office for the British Olympiad and participation in future international Olympiads now resides at Leicester. Space School UK, previously based at Brunel University has now successfully moved to Leicester and Professor Martin Ward has taken over from Professor Heinz Wolff as the Director. The first Leicester-based school was run at Easter 2000, with support from Brunel staff, and we have now taken over the full local organisation of the Easter and Summer schools.

A major new facility for schools' education, which will be available in 2001, is the Faulkes Telescope Project. This is funded by a private educational trust set up by Dr Dill Faulkes and is being constructed (and will be operated) by the Faulkes Telescope Corporation. A pair of 2-m copies of the Liverpool Robotic Telescope are being constructed. The first will be placed in Hawaii and the second on a site at the Anglo Australian Observatory, covering Northern and Southern hemispheres respectively. The advantage of these locations is that it will be telescope night during the school day in the UK. Hence, schools will be able to conduct real-time remote observations from within their classrooms, via the internet. The initial definition of the FT project was managed by the Space Research Centre and members of the XRA Group continue to play a role in the development of the project. The primary interface with schools, the Real Time Operations Centre, will be housed at the NSC and will be set up under our direction. We also have a £60,000 PPARC National Award (PI Martin Barstow) to fund the development of a teacher training programme to enhance the take-up of FT activities by schools. An important part of the project is the opportunity given to A and AS level students to conduct real research programmes with the advice and assistance of active research scientists.

Figure 3-2. Computer Aided Design image of the Faulkes telescope (courtesy of Telescope Technologies Ltd).

Matt Burleigh was the "scientific advisor" on an arts project commissioned to celebrate The Year of the Artist and bring together the worlds of Art and Science. Taking gravity as a theme, three artists from The Castle theatre in Wellingborough developed the project to explore the relationship between science and the human heart. The collaboration resulted in a performance piece entitled "Off the Wall/Out of the Case", incorporating dance, body adornment, computer enhanced imagery, poetry and 3D art works, which was performed on two nights at The Castle's Studio theatre. Each performance was followed by a discussion of the themes explored in the project. An accompanying exhibition called "Experimental Evidence" was also held throughout May 2001 in The Castle's Gallery.

An East Midlands regional branch of the British Association for the Advancement of Science has recently been created, based at the University. Members of the group have supported many local BA activities and are also involved at national level. Martin Barstow is a member of both the Physics and Education section committees, who plan sessions at the BA Festival of Science. The 2002 Festival of Science will be held at the University of Leicester.

The PPARC National and Small awards schemes provide the main source of support for our PUS activities, although some contribution is made from the "1%" of Rolling Grant funds. The Classroom Space project (PPARC National Award - £70,000; NSC - £30,000) designed to use data from real space missions to teach National Curriculum science, is now in its second year. Trials of the educational materials are currently being run in school and it is expected that these will go live on the web-site during the 2001/2002 academic year. Our schools' loan box scheme, funded by an earlier PPARC small award has been revised using summer student support and will now be operated through the NSC. A small award of £3,500 has allowed us to revise the Braille astronomy booklet included in this scheme and develop support materials for visually impaired members of the planetarium show audiences.

We have for many years operated a summer student employment scheme. In each year at least one individual has worked on PUS-related activities. For the past two years this effort has been supplemented by the Departmental Summer Undergraduate Research Experience (SURE) scheme. During the past two years we have employed 6 students in the PUS area. However, regrettably, pressure on the Rolling Grant has prevented employment of any students by XRA during summer 2001. One area where the student assistance has been particularly useful is in the development of our Educational Guide to Space website. This contains a wealth of basic information on Astrophysics and Space Science and include an "Ask an Astronomer" facility, supported by a number of group members, where we reply to individual questions posted by members of the public from all over the world. We have now dealt with approximately 700 such questions.

Communication of science to the more general public continues to be an important activity, through public lectures and assistance with coverage of science by both local and national media. The number of such events is now so large that it is impossible to account for these accurately. However, some highlights include:

Vernon Memorial Lecture (Dr M.A. Barstow), University of Delaware June 2000.

XMM-Newton article (Dr T. Roberts) in Physics Review.

Visions in Space - Exhibition of Art by Joyce Markie, Feb 2000 (held in the Department).

CURRENT SPACE PROJECTS

4.1 Introduction

This Chapter reports on completion of the instrument development programmes for Chandra and XMM-Newton, both missions now fully commissioned on orbit and delivering scientific data from well calibrated, nominally functioning instruments. Reports are provided on the first two years of the hardware phases of SWIFT and Beagle 2, as well as the successful outcome of the second J-PEX rocket flight. Information reports are also provided on the cancellation of CATSAT and the status of JET-X in the light of the current status of the Spectrum-RG mission in Russia.

4.2 Chandra Observatory

G.W. Fraser, J.E. Lees, J.F. Pearson and J. Reeves

The successful launch of Chandra on the Shuttle Columbia on 23^rd July 1999 was the culmination of a Leicester hardware involvement in the Chandra (formerly AXAF) High Resolution Camera (HRC) extending back to the very early nineteen-eighties. Our major contributions were the development of the radioisotope-free (ie. low internal background) microchannel plate glasses used in both HRC-I and HRC-S, the procurement of flight plates for HRC-S and the development of the synchrotron source as a detailed instrument calibration tool.

Post-launch emphasis has been on the exploitation of the observing time return on our hardware involvement, through visits to SAO by Fraser, Reeves and Ward (see Chapter 2 of this report). Inputs were made to the resolution of the problem of the unexpectedly high particle background in the HRC around the time of Chandra first light in August 1999. Leicester authors contributed to two HRC in-flight calibration [208, 212]

4.3 XMM-Newton Observatory

M.J. Turner, A. Abbey, P. Bennie, H. Chapman, M. Denby, J. Dowson, L. Gretton, R.G. Griffiths, A. Holland, J. Holt, A. Keay, N. Nelms, D. Ross, S. Sembay, A. Short, J. Spragg, B. Towell, D. Vernon, S. Whitehead

XMM-Newton was faultlessly launched on 10^th December1999 on Ariane 504. Commissioning of the satellite and instruments began in January 2000. All the instruments survived launch in nominal condition, and were brought into operation. From the beginning there was anxiety about radiation hazards, in particular the soft proton flux, which damaged Chandra CCDs. EPIC observed flares containing high fluxes of soft protons from first light onwards; the orbit is particularly bad from this point of view. Immediate precautions, prepared before launch, were put in place: the filter wheel was closed when the EPIC Radiation Monitor showed significant increases in radiation. This strategy was somewhat crude to start with because the ERM responds to protons above 3 MeV, while the soft protons have energies form 1-300 keV; it has been refined with time, and is now optimal, using the EPIC CCDs themselves to determine when the filter wheel should be closed, and the RGS CCDs to determine when the flux has fallen sufficiently to open it. The strategy has been completely successful: there has been no soft proton damage to the EPIC chips.

The first light exposure for the MOS cameras was of the Hickson 16 galaxy group, and this exposure amply demonstrated the ability of EPIC to generate spectrally resolved images over the full field of view (see Figures 2.6-7 and 2.6-8).

EPIC operational parameters were optimised and a series of calibration observations taken. The data taken at the Orsay synchrotron before launch were combined with spectra from Bl Lac objects and used to produce the first calibration with 10% residuals; later, observations of the Crab Nebula, 3C273, and the isolated neutron star RX J0720.4-3125 were used successively to refine the calibration, which presently has residuals below 3%, mainly around the oxygen and gold edges. At the same time monitoring and cancellation of bright pixels, and techniques for dealing with artifacts in the image were evolved. Calibration is a continuing activity: to reduce residuals in the spectrum; to develop better models of the redistribution of photon energy in the CCDs; to improve the absolute flux determination, and the energy dependence of the PSF; to extend precise calibration over the whole field of view.

The energy resolution of the CCDs was close to the Fano limit at launch and has slowly degraded as a result of hard protons penetrating the shielding during perigee passages; this is in line with pre-launch predictions, and has minimal effect so far. The sun has been very active in 2000-2001, and two solar flares have produced additional step-wise resolution changes amounting to a few months steady change each; again the cause is penetration of hard protons to the CCDs. The EPIC team monitors this and produces gain and resolution correction algorithms for the analysis software.

Once normal observations were established it was disappointing to discover that the observational efficiency was very low. In the first half of 2000, EPIC was only observing for 14 hours out of the 48 hour orbit, compared with an expectation of 37 hours. While the extra precautions necessary to protect the CCDs from soft protons contributed to this, the main cause was an unexpected inflexibility in the ESA ground system software, such that a flare lasting a few minutes caused a loss of observing time of many hours. The EPIC team refined both the radiation precautions, and, more beneficially, drastically shortened the instrument set-up sequence which was forced by the ground-segment software to be executed every time an observation re-started, even after short interruption. This, combined with operational improvements, and the introduction of the third ground station, had by January 2001 approximately doubled the observation time per orbit, to about 30 hours. Severe solar activity in the early part of 2001 has led to an observational efficiency, of slightly less than 30 hours. Progress towards the 37 hours per orbit, predicted before launch, requires a radical re-design of the ground system, which is not yet in prospect.

So far, about 11 megaseconds of MOS observations have been completed. Scientific results from early observations have been published [A&A, 2001, 365, No.1; Special Letters Issue on: First Science with XMM-Newton]. This activity has been confined almost exclusively to the instrument teams. This is because ESA has also experienced severe difficulties in preparing and releasing the data and the general analysis software to the community. The early data, incomplete and in non-standard form had to be analysed for calibration using ad hoc local software that was also used to extract preliminary scientific results. Some data are now available to the community on CDs in the correct format, and more are being released all the time.

In summary XMM and EPIC in particular is performing very well and producing excellent science. The instruments are stable and look set for the designed ten year operational lifetime. The observational efficiency needs to be further improved and there are still difficulties in getting the data out to the community.

4.4 J-PEX: High resolution EUV spectroscopy of hot white-dwarf stars

N. Bannister, M.A. Barstow, J.E. Spragg

A major outstanding question in the study of white dwarf stars concerns the relationship between the hydrogen and helium dominated groups and the interaction of these with the insterstellar medium. Of particular importance is the role He plays in the H-rich DA white dwarfs as they cool. Although He can be observed in the UV and optical bands, when present in very small quantities it is only detectable in the EUV. Furthermore, an interstellar He component can be revealed by observing its shadowing effect on a stellar EUV spectrum. However, until now, EUV instrumentation has lacked the spectral resolution capable of separating the signature of HeII from the large number of other lines (mainly Fe and Ni) present in the white dwarf spectra and distinguishing the source of HeII (photospheric or interstellar), if present.

J-PEX is a sounding rocket-borne normal incidence high resolution EUV spectrometer. Its objective is to obtain high resolution EUV spectra of white dwarf stars at EUV wavelengths. Covering the spectral range 225-245A it has a theoretical resolving power of 5000, 10 times better than EUVE. The mission is a collaboration led by the US Naval Research Laboratory, involving the University of Leicester MSSL and the US Lawrence Livermore National Laboratory. The UK effort was to supply the high spatial resolution imaging detector together with its associated readout electronics. This MCP detector stack, constructed at Leicester, was based on newly-developed small pore (6micron channel diameter) plates and was coupled to a vernier anode readout provided by MSSL. Leicester also had responsibility for defining the scientific objectives of the first flight of the instrument, to observe the hot H-rich white dwarf G191-B2B, with the aim of determining whether or not helium is really present in the star and, if found, where it is located.

The mission was approved by NASA in 1996 and development of the payload began in January 1997. Technical difficulties with the small-pore MCPs supplied by Photonis, which produced unexpectedly low quantum efficiencies and problems with the instrument stability during calibration, delayed the first flight of the spectrometer until February 2000. The Photonis MCPs were replaced with larger-pore devices from earlier stock, which met the QE requirements but with a consequent small degradation of the imaging performance and, as a result, spectral resolution. Further work with Photonis on the problem has not yet produced a solution to the QE problem. The instrument stability problems were produced by internal heating of the payload during the long test exposures, required to build up photon counting statistics, causing some flexure of the spectrometer. This was not expected to be a problem during a short duration flight and the measured spectral resolving power of 2500-3000 was believed to be a lower limit on the true value.

J-PEX was first flown from White Sands Missile Range, New Mexico, on board a Terrier-boosted Black Brant Vc sounding rocket on 25^th February 2000. Unfortunately, the rocket drifted outside the boundary of the range and the flight was terminated from the ground 2 seconds before burnout. The explosion from the termination charge caused the payload to tumble and, although stability was restored by the ACS no gas remained for pointing the telescope and no science data were obtained. However, the detector, payload electronics and mechanisms all functioned as anticipated and the experiment was recovered in good condition after deployment of the parachute. The flight problem was later attributed to highly variable upper atmosphere winds and overcorrection of the launcher azimuth setting for the actual conditions during flight. A compensatory second launch was offered by NASA and new procedures were implemented for the wind-weighting.

Figure 4.4-1. Image containing the four spectra of G191-B2B recorded during the flight of J-PEX. The bright spot at location [X=220, Y=210] is the image of G191-B2B produced by the co-aligned EUV mirror. All photon positions have been corrected for the effects of small ACS drift motions, by using data from this mirror and the optical telescope.

The detector was refurbished for the second J-PEX flight and, following reintegration in the payload and recalibration of the spectrometer, the instrument was launched on February 22nd 2001 (see Cover). On this occasion, the boost phase was nominal and G191-B2B was acquired without any problems and observed for 303s before the payload was shut down for re-entry. Real time images from the spectrometer, EUV tracking telescope and CCD optical camera showed that the target was well-centred and tracked with low drift-rate by the Mark VID ACS (necessary to achieve high spectral resolution). The four spectra (one from each of 4 gratings, see Figure 4.4-1) were clearly visible within a few seconds. Since the flight, Leicester has had the responsibility of reducing and analysing the spectral data with assistance from NRL and MSSL. We are still in the early phase of the scientific analysis, but the composite spectrum (sum of the 4 gratings, see Figure 4.4-2) shows a number of clear features which we can identify with (variously) HeII, OVI and FeV. The spectral resolving power achieved is ~4000, making this the highest resolution spectrum ever obtained in soft X-ray and EUV wavebands.

Figure 4.4-2 High resolution EUV spectrum of G191-B2B, obtained with the J-PEX spectrometer, spanning the wavelength range 221-244 Å (error bars). The histogram is the best-fit theoretical model of the star and ISM, as described in the text. The strongest predicted lines of He, C, N, O, and P are labeled with their ionization state and wavelength. Lines of Fe and Ni are too numerous to include here and account for the unlabelled individual features and broader absorption structures.

4.5 SWIFT

A. Wells, A.D. Short, A.F. Abbey, R.M. Ambrosi, H.E. Chapman, J. Dowson, G. Peters, D. Ross, J. Spragg, T. Stevenson, B. Towell, M.J.L. Turner, D. Vernon, M. Ward, D.J. Watson, R. Willingale

Swift is a NASA MIDEX mission to detect Gamma Ray Bursts (GRBs) and to study their afterglow in the X-ray and UV/optical wavebands. By locating each burst with sub-arc-second resolution, measuring light curves over a period of minutes and hours and by detecting spectroscopic lines, Swift will help us to identify the progenitors of these extraordinary events.

4.5.1 Swift Science

Astronomical bursts of gamma rays were discovered in the late 1960s. They are now established to have an isotropic distribution over the sky and to lie at cosmological distances. Even allowing for considerable beaming, the energy emitted by a GRB must be more than ~10⁵¹erg. This and the short time-scales indicate a process involving compact, massive objects. Leading theories are the merger of a binary pair of neutron stars or the collapse of a giant, spinning star in a ‘hyper-nova’. Both models result in the creation of a black hole and propose that the high angular momentum of the system enables a significant fraction of the prompt radiation to escape. In addition, the resulting black hole in both models is orbited by a torus of neutron-density material, which is a powerful engine for extended (afterglow) emission. A possible distinction between the models is the predicted time scale with one expected to emit Gamma Rays for just a few seconds and the other for several tens of seconds. It is already clear from CGRO data that GRBs fall into at least two temporal populations and it is therefore possible that both models are at least partially correct, describing two distinct types of GRB.

The current phase of Gamma Ray Burst study has been dubbed the ‘afterglow era’ because the key to identifying GRB progenitors lies in multi-wavelength observations of burst afterglows. Breaks in the X-ray and UV/optical light curves will indicate key events in the evolution of each burst. Spectroscopic features will yield the composition of the progenitor and/or the environment into which it is expanding as well as providing red-shift measurements. In addition, simply locating optical counterparts with sufficient precision will help to distinguish between models since hyper-novae are expected to occur near star forming regions whilst binary pairs of neutron stars are likely to have drifted far from any galaxy.

4.5.2 The Swift Gamma Ray Burst Observatory

The Swift Gamma Ray Burst Observatory (Figure 4.5-1) will detect Gamma Ray Bursts at a rate of approximately one per day. The primary objective is to report the location of each new burst to the astronomical community within ~5 minutes of the initial detection. If the burst has an optical counterpart/afterglow, the location will be reported with sub arc-second resolution. The second objective is to measure the X-ray and UV-optical light curve of each new burst from initial acquisition for a period of hours or days. Some bursts will also be revisited periodically to extend the light curves over a period of weeks.The third objective is to study spectral features (particularly in the X-ray band) and to monitor their evolution as the afterglow decays.

Swift is due for launch in the autumn of 2003 on a Delta II vehicle from Kennedy Space Centre. It will be placed into a 600km altitude, 19^o inclination orbit. The design lifetime is 3 years. The orbit lifetime is in excess of 5 years. Communications will be primarily via the TDRSS network and the Malindi ground station. The Science Operations Centre will be located at Penn State University. A UK Swift Science Data Centre will be maintained at the University of Leicester. The Swift principal investigator is Dr. Neil Gehrels of Goddard Space Flight Centre and the prime spacecraft contractor is Spectrum Astro.

Swift will carry three instruments. The wide field, gamma ray Burst Alert Telescope (BAT) provided by Goddard Space Flight Centre has coded aperture optics and Cd(Zn)Te detectors. It will monitor the sky over 2sr and detect each new gamma ray burst, reporting its position to the spacecraft with arc-minute resolution. The Spacecraft will then slew autonomously to point two co-aligned narrow field instruments, the X-ray telescope and the UV/optical telescope. The UV/optical telescope is based closely on the Optical Monitor aboard XMM-Newton. It is being produced by MSSL in collaboration with Penn State University.

Figure 4.5-1. Swift Gamma Ray Burst Observatory

4.5.3 The Swift X-ray Telescope (XRT)

The Swift X-ray telescope [293] has a field of view of 23.6 arc-min, an effective area of 110cm² at 1.5keV and an energy range of 0.2-10keV. The PSF half power diameter is 15 arc-sec at 1.5keV. It is being provided through a collaboration between Penn State University (the lead institute) the University of Leicester and Osservatorio Astronomico di Brera. PSU are responsible for the project management and are providing the telescope tube, telescope door, and most of the GSE. They are also responsible for system engineering (sub-contracted to Swales Aerospace), electronics (sub-contracted to South West Research) and software (sub-contracted to Preschutti Associates.) Brera are providing the X-ray mirror, which is the flight spare from JET-X.

The University of Leicester is responsible for providing the focal plane camera, the telescope alignment monitor, the electron deflector and has a leading role in the telescope design and also the optical interface. The University will lead much of the telescope integration and alignment and will support qualification, calibration, spacecraft integration and post launch operations. In addition the University of Leicester has made significant contributions to the system engineering, particularly in the thermal design.

4.5.3.1 Focal Plane Camera

The focal plane camera housing (Figure 4.5-2) is a vacuum cryostat, which facilitates cold testing of the CCD and enables launch of the optical blocking filter under vacuum. The cryostat incorporates a HOP actuated door (single shot on-orbit) and vent valves. The CCD cold finger is thermally isolated from the camera housing by means of glass fibre and G10 supports, vacuum being maintained by a thin stainless steel diaphragm. The cold finger itself is a substantial 5.4kg of Al, which surrounds the CCD, doubling both as a heat-sink for the thermoelectric cooler and as a proton shield. The housing is constructed in two parts such that the main PCB may be sandwiched between them with O-ring seals. All electrical feed-throughs are via the inner layers of the PCB. The cryostat is mounted on a conical stand off structure, which incorporates the telescope out-gassing baffle. The stand-off structure is mounted onto the telescope tube through a shim. The thickness of the shim will be adjusted to set the telescope focal length. All of the cryostat mechanical components are fabricated and have been fit checked. They are currently undergoing Nickel and Gold plating, tapping, welding etc. in readiness for final assembly.

Leicester is responsible for the CCD front-end electronics (essentially the pre-amplifiers) and those electrical and electronic components internal to the camera which are associated with monitoring and mechanism operation. This includes the main front-end board, the sun shutter driver board and numerous smaller boards and connectors for the hall sensors, pressure and vacuum monitors and HOPS. All boards, components, wire and connectors have been fabricated/procured. Board population and wire bake-out is underway.

The detector [236, 327] is a CCD22 identical to those flown on XMM-Newton [148]. It has an image section of 600x600 pixels giving 2.4 arc-sec/pixel in the Swift focal plane. Thanks to an open electrode structure [146, 263] and high resistivity silicon, the quantum efficiency exceeds 20% from 200eV to 12keV. Extensive radiation damage studies have been conducted for orbital inclinations up to 22^o [273](Abbey et al 2001). With the resulting shielding configuration and the current 19^o orbit, the CCD will meet the XRT resolution requirement (<300eV FWHM at a photon energy of 6keV and a CCD temperature of -100^oC, at end-of-life) with a substantial margin. The flight and flight spare detectors have been selected. The flight detector is currently undergoing calibration in the X-ray test facility at Leicester.

The CCD assembly also incorporates a 5 stage thermoelectric cooler (TEC), an Al/Be TEC mount, a low conductivity flex circuit and an indium soldered connector. The first units have been integrated at Leicester, and are undergoing a rigorous test and qualification programme including glue bond trials, thermal cycling and vibration.

The camera incorporates a single, mesh-less filter. This comprises 1800Å polyimide and 480Å Al and is slightly thicker than the EPIC thin filters (410Å Al). The filter has been specified such that Earth-shine will contribute of order 1eV to the FWHM at a limb avoidance angle of 30^o. Flight specification and engineering model filters have been procured. X-ray transmission will be checked by measuring camera quantum efficiency with and without the filter in place and fitting with simple transmission models.

The camera incorporates four ⁵⁵Fe sources. These irradiate the CCD corners outside the field of view allowing the resolution, gain and charge transfer efficiency to be monitored continuously throughout the mission. The source X-rays are always present in the data but can be removed in all modes except the fastest timing mode. Since this mode is reserved only for spectroscopy at the highest fluxes, pollution due to the corner sources is insignificant. The calibration sources have been procured and tested.

The camera incorporates an autonomous sun shutter, which will not be closed in orbit except in the event that the spacecraft loses attitude and points towards the sun. It is a simple blade mounted on a stepper motor, which is independently powered and triggered by an array of solar cells mounted inside the telescope tube. All of the components including the motor, the blade, the solar cells and the solar sensor have been procured. The solar cell mounting is being finalised and the motor is being evaluated.

Figure 4.5-2. Swift XRT Focal Plain Camera

4.5.3.2 Electron Deflector

The electron deflector is an array of magnets mounted on an Aluminium spider, which sits just behind the telescope mirror. The design is a scaled down version of the XMM electron deflector. It essentially prevents any electrons from reaching the CCD, which would otherwise contribute to the background. The deflector magnets have been procured. The spider support is in the final stages of fabrication.

4.5.3.3 Telescope Alignment Monitor

In order to locate GRBs with ~arc-sec resolution, the XRT requires an alignment monitor to reference the telescope bore-sight to the star tracker bore-sight. This is a Leicester subsystem comprising a light source, a number of optics and an active pixel sensor camera, which is being developed by Sira Electro-Optics Ltd. The optics and associated mechanical mountings are currently being procured/fabricated.

4.5.3.4 Mirror Module

The XRT mirror is the flight spare mirror from the JET-X programme. It is being provided by the Osservatorio Astronomico di Brera but the interface with PSU and much of the system engineering is the responsibility of Leicester. The response of the mirror has been re-measured at the Panter facility [272] to ensure that it had not changed whilst the mirror has been in storage. These data are also being used to develop the centroiding algorithms for the X-ray telescope [272]. The mirror support structure and baffles are currently at Goddard Space Flight Centre undergoing qualification testing with an STM mirror.

4.5.3.5 Integration Alignment and Qualification

The integration, alignment and qualification of the XRT will take place at GSFC, commencing early in 2002. The integration and alignment of the optics in particular, is a Leicester responsibility drawing on experience and procedures developed for the JET-X project. Functional testing of the focal plane camera will also rely heavily on XMM-EPIC GSE and experience.

4.5.3.6 Calibration

CCD calibration is already underway. The mirror response has been re-measured and the optical filter will be characterised once the camera has been assembled. These elements are being combined at Leicester in order to generate the initial telescope response (Figure 4.5-3). A full end to end calibration of the telescope including mode dependencies is scheduled to take place in 2002 at the Marshall Space Flight Centre.

Figure 4.5-3. Swift XRT total effective area

4.6 Beagle 2

M.R. Sims, G. Butcher, J. Dowson, B. Favill, G.W. Fraser, J. Holt, N. Nelms, D. Pullan, D. Ross, J. Sykes, A.A. Wells, S. Whitehead

Beagle 2 is the innovative 60kg lander, due for launch as part of the ESA Mars Express mission in June 2003, arriving on Mars in late December 2003. Beagle 2 is the Space Research Centre’s first approved mission in planetary science. Beagle 2 surface operations are planned for 180 Sols (Martian days), which may be extended up to 1 Martian year.

The project is funded by a variety of sources - ESA, DTI and sponsorship - however the UK science instrumentation funding is mainly provided by PPARC. Beagle2, named in commemoration of the ship which carried Charles Darwin on his voyage around South America, will examine the geomorphology and geochemistry of the landing site in the Isidis basin as well as searching for evidence of life using isotopic fractionation of carbon as a bio-marker (biological signature) for extinct life, and the detection of atmospheric methane as a bio-marker for extant life. Isidis appears to be an impact basin, which has apparently been filled with sedimentary type deposits and so represents a good site in which to look for evidence of life. Beagle 2 carries experiments from the Open University (the lead science institute), Leicester, University College London, Germany, Switzerland and Hong Kong. Astrium UK (Stevenage) is the prime industrial contractor.

The Leicester Space Research Centre is responsible for a leading role in the management and systems engineering in Beagle 2 and for provision of two instruments. The responsibilities are as follows:

1. Top level management of the project via the post of Mission Manager (Dr M.R. Sims) with special responsibility for the science instruments and Flight Operations and Ground Segment Planning.

2. The management of the instrument interfaces and schedules.

3. The X-ray Spectrometer (XRS) (PI : Prof. G. Fraser), measuring the elemental composition of the surface and rocks using X-ray fluorescence analysis.

4. The Environment Sensor Suite (ESS) (PI : Dr. M. Sims). This is a joint project with Dr. J. Zarnecki’s group at the Open University. The ESS measures local weather and dust conditions and includes the first planned measurement of the UV spectrum on the surface of Mars.

5. The design, integration and test of the integrated instrument package, the so-called PAW, located at the end of the Beagle 2 robotic instrument arm and consists of three instruments and a number of associated tools and support systems.

The design phase of the project has been completed and flight hardware construction is advancing rapidly. Development models and, in some cases, qualification or flight models of some instruments have been delivered and are under test and calibration. In the case of the Leicester instruments, a development model of the XRS is currently under test with the FM build to commence imminently. Similarly, development models of the individual environmental sensors have been built and flight models are under construction. A Structural Model (SM) of the PAW has been built and tested ; the Structural Thermal Model (STM) is now in manufacture. The PAW breadboard electronics have been tested and the flight model is now in construction. Figure 4.6-1 shows the SM PAW. Figure 4.6-2 shows the breadboard PAW electronics constructed and tested at Leicester.

Studies are underway, led by Dr Sims, to determine the operational requirements for Beagle 2. Our favoured option is to locate the Lander Operation Centre for Beagle 2 in the Space Research Centre’s facilities at the National Space Centre, thereby bringing Public Understanding of the Science of Beagle 2 to the wider general public, as well as developing outreach educational projects for schools around this unique project.

Figure 4.6-1. Beagle 2 Structural Model PAW

Figure 4.6-2. Beagle 2 PAW Breadboard electronics

4.7 CATSAT

C.Whitford, C. Bicknell, H. Chapman, D. Ross, D.J.Watson

NASA instigated a critical design review of CATSAT, at the end of 2000. The review identified three concerns which were considered to threaten the mission. These were immature development, qualification and verification status of the spacecraft (UNH responsibility); long lead time of replacement avalanche photo-diodes (APD) for the X-ray detectors (Leicester has been responsible for the APD test and verification programme); high risk of schedule slip which would impact on the launch schedule of NASA’s ICESAT mission, with which CATSAT was due to be launched. The CATSAT recovery funding plan ($2M), submitted in April, was rejected by NASA, citing unacceptable risk to the ICESAT mission as the main reason. Accordingly the CATSAT launch, with ICESAT was cancelled by NASA and the PI was instructed to complete and to mothball the CATSAT spacecraft.

Leicester has undertaken to round off the current work on the APD detectors and to delivery the detector modules to UNH. Leicester’s programme on the CATSAT spacecraft and instruments has been supported through a direct contract from UNH. PPARCD has not been supporting the CATSAT hardware programme and no PPARCD resources have been used.

As part of its education remit, CATSAT was to have been operated from two ground stations, one located at Leicester at the National Space Centre. This facility has been built, with NSC and UNH resources. No longer required for CATSAT, the Control Centre is now being set up for use with other missions, and it is proposed that from next year, the Beagle 2 Lander Operations Centre will be housed in the facility.

FUTURE PROJECT STUDIES

5.1 High Energy Astrophysics

5.1.1 X-ray Early Universe Spectrometer (XEUS)

M. Turner, A. Holland, M J Ward, R. Willingale

XEUS, succeeding Chandra and XMM-Newton, is dedicated to the study of the evolving hot Universe. It provides high-resolution X-ray spectroscopy and imaging, with an aperture of 6 m² - later to increase to 30 m²; the energy range is from 0.05 keV to 30 keV. Under study as part of the ESA Horizons 2000 programme, XEUS will be an evolutionary and long-life X-ray observatory, evolved and upgraded via the ISS. Because of its large aperture and focal length, XEUS will comprise separate focal-plane and mirror spacecraft flying in formation. XEUS can detect objects as faint as 4x10^-18 erg/s/cm² in its final form, and resolve iron lines in typical AGN, at z=10, allowing the evolution of accretion power in the Universe to be traced back to a few percent of its present age. XEUS can trace the evolution of clusters from the first groups of galaxies, and metals synthesis down to the present epoch; it can establish the physical properties of material in dark-matter dominated structures. XEUS cannot be achieved without serious and lengthy technology development, and a major allocation of resources; hence it is seen as a global strategic programme, initiated by the European Space Agency, and bringing together the efforts of the world's space scientists and agencies. XEUS is conceived as a two-stage mission: XEUS 1, with an aperture of 6 m²; and XEUS 2, having an aperture of 30 m².

The preparations for the XEUS mission are being conducted under the guidance of a steering committee, chaired by Dr Martin Turner (Leicester). The activities are carried out by working groups in astrophysics, detectors, & optics; the system design is led by the ESA study scientist, supported by industry. The astrophysics working group report and the mission report have already been issued by ESA and the detector and mirror reports are due to be issued in September. Dr Andrew Holland and Dr Richard Willingale from Leicester are members of the detectors and mirrors working groups respectively.

In parallel with system-level and mirror studies, the key technologies for the focal plane are being developed, mainly with national funding. For spectroscopy, making use of the very high flux collected by the XEUS mirrors, cryogenic detectors are the most promising. Imaging the early hot Universe requires moderate spectral resolution over a wide field of view; advanced CCD technology to cover the large focal plane, and handle the large flux coming from the mirror, is being developed from the MOS & PN technologies used on XMM-Newton.

5.1.2 Lobster-ISS

G.W. Fraser, A.N. Brunton, N.P. Bannister, J.F. Pearson, S. Whitehead and G. Price

Lobster-ISS (Fraser et al, SPIE 4497 2001) was proposed to the ESA F2/F3 opportunity in January 2000 as a Space Station attached payload. The concept of an imaging all-sky X-ray monitor based on Angel’s lobster-eye principle had been under development by a core consortium of UK, US and Australian groups for some time. In 1997 a proposal was made to the NASA SMEX AO for a free-flier version of the telescope. That proposal was favourably reviewed in the 1997 PPARC bilateral line although NASA rejected the SMEX proposal on the grounds of the technical immaturity of the microchannel plate optics and detectors.

By the end of the present reporting period, Lobster-ISS, an instrument with a UK PI (Prof G.W. Fraser) had been approved for flight by the ESA Science Directorate, had undergone a successful ISS accommodation study and was approved to enter a one-year ESA-funded (0.4 Meuro) Industrial Phase A study, due to begin in January 2002. It was also the only post-XMM, pre-XEUS X-ray astrophysics experiment approved in Horizon 2000+ and a possible entry point for UK industry to the International Space Station programme. Lobster-ISS consists of six X-ray telescopes based on square-pore microchannel plate optics developed over a number of years within the PPARC-funded laboratory programme at Leicester. The major design effort during the accommodation study was to repackage the telescopes into the volume limit of the ISS Express Pallette Adapter with minimum sensitivity loss.

The goal of Lobster-ISS, as for any all-sky monitor, is to approach the limit of "all the sky, all the time". The instrument consists of six MCP telescopes, collectively providing wide-angle (22.5^ox162^o) X-ray imaging in the 0.1-3.5keV energy band, covering almost the entire X-ray sky once per 90 minute ISS orbit. For comparison, the instantaneous fields-of-view of XMM-Newton and Chandra are less than 1 degree diameter.

Commitment to the flight instrument build is now scheduled for the second quarter of 2003, instrument delivery for 2007 and launch for 2009. Operations will last for three years.

5.1.3 Astro-E

M.J.L. Turner

Astro-E is the Japanese ISAS mission in X-ray astronomy that follows ASCA. Its main thrust is high-resolution spectroscopy using imaging X-ray telescopes coupled to CCDs and a novel imaging X-ray microcalorimeter. There are five foil mirror X-ray telescopes, four with CCDs at the focus, and one with a cryostat containing the micro-calorimeter. The micro-calorimeter is provided by GSFC. Leicester was invited to provide the CCD cameras, but PPARC was unable to fund this; eventually CCDs were provided by MIT-Lincoln; Dr Martin Turner (Leicester) remains a member of the Astro-E Science Working Team, providing advice and consultation on science objectives, and on the CCD cameras. Astro-E was launched in February 2000, but unfortunately, a failure in the first stage of the M-V rocket led to it not achieving orbit. Since this event, the cause of the failure has been thoroughly analysed, and modifications to the launcher made. ISAS has been funded by its ministry for a re-flight of Astro-E in 2005, and the science working team met in Tokyo in May to reconfirm the mission and its scientific aims. Astro-E is mainly a Japan-US collaboration, and NASA has now agreed to the funding of the US component: the reflight of the mission is therefore now fully approved. As a member of the Science Working Team Leicester has access to the guaranteed time programme with a modest amount of observing time. This has been reconfirmed for Astro-E II.

5.2 Planetary Science Missions

M.R. Sims, G.W. Fraser, D. Pullan, J. Sykes, S. Whitehead, A.N. Brunton

This work is targeted at future planetary missions within the ESA and NASA programmes to Mercury, Mars and the Near Earth asteroids, with a developing emphasis in Astrobiology.

In the area of microchannel plate X-ray optics, the demonstration of a working Wolter Type I telescope geometry along with development of near-room-temperature GaAs pixel arrays by collaborators at ESA ESTEC, has led to the design of an imaging X-ray fluorescence spectrometer - HERMES - for elemental mapping of the surface of Mercury, using the solar X-ray flux as the primary excitation. HERMES has been submitted to the current PPARC pre-selection round for the ESA BepiColombo Cornerstone. The HERMES instrument concept is shown in Figure 5.2-1

A joint project with Cranfield University, funded by EPSRC, will start in September 2001 to investigate the application of modern bio-sensor technology in the detection of bio-markers (biological signatures) on other planets. This project will utilise the technology of molecular imprinted polymers to directly detect molecules of given shapes to produce an IC sized sensor package. In the initial work, four target molecules, have been selected using the expertise of Prof. W.D. Grant of the Department of Micro-biology and Immunology at the University of Leicester, a co-investigator in the project. The target molecules include one with a chiral nature (i.e. with a specific stereo chemistry) a protein (isoleucine), a constituent of cell membranes (C₂₀ isopranoid), and a control target molecule (mellitic acid) formed in the decay of meteoritic organics. All of these are preserved within rocks on time-scales of >10⁶ years on Earth. Figure 5.2-2 shows an artist’s impression of the bio-sensor chip which will be constructed by the Bio-technology Centre at Cranfield. The Space Research Centre will test and package the development sensor, and in particular will examine the effects of radiation damage and temperature on the performance of the devices. This work has a number of potential industrial applications including monitoring of biological contamination.

Figure 5.2-1. HERMES schematic

Figure 5.2-2. Cranfield Bio-sensor Chip, approximately 2cm on a side. Sensor pads utilise resistance and optical measurement techniques. Some control pads without molecular imprinted polymers are included into the design.

5.3 Optical and Infrared Astrophysics Missions

5.3.1 Next Generation Space Telescope (NGST)

J Pye, A Holland, P O'Brien, T Stevenson, M Ward.

The Next Generation Space Telescope (NGST) will be the successor to the Hubble Space Telescope (HST). During 1999, the consortium [Marconi Space (Toulouse), University of Leicester, and Dornier (Ottobrun)] undertaking the study, for ESA, of the Visible Wavelength Camera / Spectrograph, completed its work, with Professor M. Ward as the science lead. A comparison of CCD and pixel-array detector technologies was made. The CCD option was ultimately excluded due to its relatively high operating temperature of ~140K which would produce a thermal load to the other instruments operating at 30K. The key limitations of the pixel-array detector technology were identified for follow-up work during the later spacecraft definition and development phases. The visible wavelength instruments were later dropped by NASA from the NGST baseline mission, in favour of solely near- and mid-infrared instrumentation, which provide maximum sensitivity for the NGST primary science goals.

Leicester is now one of the core members of the European consortium which will develop the Mid-Infrared Instrument (MIRI) jointly with NASA. The MIR instrument consists of an imaging camera and a spectrometer. It will be developed with roughly equal resources from Europe (coordinated by ESA) and NASA. The European funding will be largely from national agencies. Leicester is working closely with the ATC Edinburgh - the European lead institute (European Co-PI Dr G. Wright), and the other UK core partners (Astrium UK and RAL) in defining the programme for the MIRI Phase A studies, due to start formally in October 2001.

5.3.2 GAIA & Eddington

A Wells, A Holland, I Hutchinson, A Keay, J Pye.

We have taken a strategic decision to broaden our interests in the use of space-qualified CCD detectors to extend into the optical waveband. We are well placed to offer essential insights into areas such as packaging, mosaicing and radiation effects for space-borne CCDs, based on our experience as the PI group for the EPIC X-ray CCD cameras on XMM-Newton. We are supporting the current `Phase A' definition studies of GAIA (an ESA cornerstone mission, for astrometry and dynamics of the Galaxy, due for launch 2010-2012) and Eddington (an ESA `reserve' mission, for stellar structure and extra-solar planet finding, due for launch 2007 if given full funding approval). At the invitation of the lead scientists in each mission we are participating in the ESA Scientific Working Groups for GAIA, and in the Eddington EddiCam consortium.

LABORATORY RESEARCH

6.1 Introduction

The laboratory activities housed in the Space Research Centre have continued to grow in ambition and collaborative scope during the present reporting period.

The laboratory programme has always been strongly coupled to Industry through schemes such as PIPSS, CASE and ROPA. A completely new strand has been added in the recent appointment of M. Ahad to the post of TCS (Teaching Company Scheme) associate, a joint appointment with JRA Aerospace and Technology Ltd (Marlow, Bucks). The goal of this associateship is to assist in the transfer of technology from the Leicester programme into other areas of science and into industry. Technology transfer across the life sciences interface has led to the appointment of J.E. Lees to the post of Research Fellow within a University BioImaging Unit housed in the Space Research Centre. The opportunities in multi-disciplinary research continue to grow, with the very large scale cross-council Basic Technology programme seeking proposals in September 2001. The management of the activities described in the following sub-sections will have increasingly to balance the requirements of future missions in astrophysics and, now, planetary science, while exploiting new opportunities for enhanced funding outside these fields.

Finally, we have succeeded, in the case of Lobster-ISS, in bringing a technology - microchannel plate X-ray optics - from the very first basic measurements in 1993 to a point where it now underpins a mission selected by ESA for Phase A study. This example illustrates the rationale for continued Rolling Grant funding of instrumentation development extremely well.

The following sections describe the achievements in the three main areas of our laboratory programme.

6.2 Microchannel Plate (MCP) Optics and Detectors

Major developments in these areas have been:

1. The outgrowth of the Lobster-ISS all-sky monitor proposal from basic measurements in square-pore MCP optics (See Section 5.2).

2. The demonstration, for the first time, of focusing from an MCP approximation to a Wolter telescope, some seven years after its first description by us in the literature. This demonstration was the culmination of a large scale (three-year, 0.75M euro) ESA Technology Research Programme with Photonis SAS, the MCP manufacturers. The prototype Wolter optic and the measured 1.7 arcminute focus, at an energy of 8 keV, are shown in Figures 6.2-1a,b [186-188].

3. The evaluation of MCP detectors with ultra-small pores [223] produced within the same TRP. These plates were baselined for J-PEX [176], but were ultimately replaced because of problems with the quantum efficiency in the EUV band.

4. The commencement of a major EPSRC-funded programme to produce an imaging X-ray fluorescence spectrometer based on an MCP relay lens and an open-electrode X-ray CCD. This programme has Gresham Scientific Instruments as its industrial partner [91, 92].

5. The establishment of the BioImaging Unit to exploit spin-off imaging technologies, beginning with the large area, low background MCP detectors developed for Chandra [82-84]. Commencement of a major collaboration on bioimaging with the MRC Centre for Mechanisms in Human Toxicology and Bayer Pharmaceuticals. Figure 6.2-2 shows a pair of two dimensional protein gels registered by the Leicester MCP detector. On the left is a control map of brain proteins - the vertical axis is mass and the horizontal axis is charge state. Each bright point (seen by its tritium emission) is a protein. In the image to the right, the brain tissue has been exposed to an organophosphate poison and certain proteins are missing.

6. Collaboration with the Daresbury laboratory in the design and construction of a fast electron detector for the TEARES toroidal analyser. This has involved the generation of a new anode design based on the CODACON principle.

Figure 6.2-1a. MCP Wolter optic, 6 cm in diameter

Figure 6.2-1b. Focus measure in the Leicester 20m X-ray beamline

Figure 6.2-2. Tritium labelled 2-D electrophoresis gels

Figure 6.2-3. Prototype auroral imager MCP

6.3 Astro-G

We have been investigating the development of CCD technology for the Astro-G spacecraft (now called NeXt). The NeXT spacecraft will be the next in the series of the Japanese X-ray missions and will specifically cover astronomy in the hard X-ray region of 5-100 keV through the use of multilayer optics. This application requires detectors which efficiently cover the energy band 1-100 keV. The detector concept consists of a hybrid imager formed from an X-ray CCD, providing high-efficiency detection with high-resolution spectroscopy in the 1-10 keV band, over a high-Z pixel array detector, such as CZT, performing imaging and medium resolution spectroscopy in the 10-100 keV band. In collaboration with MAT Ltd (formerly EEV), we developed a detector with deep depletion, fabricated on high resistivity bulk silicon, where the majority of the optically "dead" substrate layer was removed through a thinning process. The resulting detector was aimed at demonstrating the hybrid imager concept and was packaged on a special carrier with laser-cut hole in the base. Figure 6.3-1 shows the arrangement used during the testing of the detector, together with our CZT diode which was used for beam calibration and silicon absorption tests. The test proved successful demonstrating that MAT could manufacture a detector with substrate removed. In combination with our other work into ultra-depleted CCDs with 220 microns depletion (section 6.4) this approach provides demonstration of the technology needed for the NeXT spacecraft. 6.3-2 shows the predicted X-ray quantum efficiency of a future hybrid detector formed from a combination of an ultra-deep depleted CCD with substrate removed, above a high-Z CZT detector.

Work on the spacecraft is currently in abeyance due to the Astro-E2 re-flight opportunity, but the technique is now being considered in other applications, such as the XEUS wide field imager.

Figure 6.3-1. Pictures showing the test setup for our Astro-G detector trials. The CCD22 was a spare detector from the XMM/EPIC batches, fabricated on bulk silicon. The silicon CCD was thinned prior to being packaged to remove the bulk of the un-responsive substrate silicon. A reference CZT detector was placed behind the CCD for reference and total throughput measurements.

Figure 6.3-2. X-ray quantum efficiency of a future hybrid detector formed from a combination of an ultra-deep depleted CCD with substrate removed, as demonstrated under our rolling grant, above a high-Z CZT detector.

6.4 Cryogenic Detector Development

This programme aims to develop efficient (quantum efficiency, QE > 50% at 6 keV), high count rate (~kHz per pixel), non-dispersive imaging spectrometers capable of energy resolution, deltaE ~ 2 eV in the 0.5-7 keV energy band. Such a detector is essential for future X-ray observatories, for example for the narrow field instrument for XEUS (X-ray Evolving Universe Spectrometer), now under study by ESA and Japan. Our work is part of the UK X-ray Cryogenic Spectrometer Programme (XCSP) funded by PPARC.

Our detector fabrication is in collaboration with the Thin Films Group of Oxford Instruments Superconductivity, a company with world-leading expertise in cryogenic detectors. The microcalorimeter technology pursued at Leicester is the transition edge sensor (TES) with electro-thermal feedback, pioneered in the United States by the NIST Boulder group. The key TES element is a superconducting film, voltage biased within its superconducting-to-normal transition. Our initial detector development used Al/Ag TESs fabricated by our industrial partner, Oxford Instruments Thin Films (Cambridge). Aluminium/Silver was the proximity bi-layer then favoured by NIST and all other groups in the field. Our work quickly showed, however, that these films were not stable, due to oxidation and the miscibility of the silver and aluminium [71]. This has forced groups around the world to seek alternative technology for TES fabrication. Several groups are now investigating bi-layers formed from "immiscible" normal and superconducting metals such as Ti-Au, Mo-Cu, Mo-Au. Ultimately, these films suffer from fabrication artefacts at the film edges, requiring design iterations to lessen the impact of the edge effects. The most serious shortfall of these materials is in the reduced critical current of the manufactured film (current required to force the film out of the superconducting state). The critical current is linked through power dissipation to the ultimate count rate of the detector. Due to the high throughput nature of the proposed future missions, detector count rate will be one of the key parameters in comparing future detectors.

In our work we concentrated on the development of a single-film TES based on Iridium. The film reliability issues are thereby avoided, with only the interconnection technology posing potential remaining problems. Figure 6.4-1 shows a single pixel sensor and gives the superconducting transition curves for a number of Ir-TES samples grown under different conditions (Trowell PhD Thesis 2001). A degree of control is demonstrated over the superconducting transition temperature, which will enable devices to be fabricated to operate at a specific temperature in the range 50-150 mK. This approach toward producing a TES with tuneable transition temperature is the subject of a patent application by Oxford Instruments.

The reliability of the Ir system has been evaluated and initial measurements indicate that it is satisfactory for use in a long duration space mission. Figure 6.4-2 shows changes in device resistance measured at elevated temperatures which can be used to predict a 10% change in resistance at room temperature after ~400 years. The reason for the change in performance is believed to be due to oxidation of the Nb tracking on the detector which may be avoided in future detectors through use of a passivation layer.

In addition to the development of the single pixel spectrometer based on the Ir-TES, we have also performed an investigation into an imaging detector. There are currently two major drives toward imaging detectors; arrays of pixels, or distributed detectors, where spatial information is based on the heat distribution within an absorber. This type of imager is referred to as a Distributed Read-Out Imaging Device (DROID). For astronomy applications, where the image is a point source, the count rate difference between the approaches is only ~2-5x. Figure 6.4-3 gives a photomicrograph of the first DROID produced under this programme (July 2001). This device comprises a sheet absorber of width 250 microns, to match the PSF of the XEUS optic, and a length of 4.8 mm. The detector sits on a Si₃N₄ micro-bridge which provides thermal isolation from the base plate which is at ~20-50 mK. An array of such linear detectors (side by side) would thereby produce an imaging detector of ~5x5 mm² capable of a lateral position resolution of <200 microns and a vertical resolution at the 250 microns pitch required by XEUS (in fact the lateral resolution is modelled to be better than 50 microns). The 1-D DROID is read out using two identical Ir TES’s at each end of the absorber. Device testing is currently underway to investigate both energy and spatial resolution of this device. However, initial testing in Goddard of a device with a similar structure has demonstrated that both imaging and spectroscopy of the photons can be achieved with high spectral resolution. Future work will be targeted at obtaining X-ray high resolution X-ray spectra from our single pixel devices in conjunction with the development of a 2-D imaging prototype using the DROID approach.

Figure 6.4-1. Picture showing a single pixel Ir-TES manufactured by Oxford Instruments, together with transition curves showing resistance vs. temperature for Ir resistors grown under different conditions. This produces a controllable transition temperature, Tc, which determines energy resolution vs. heat capacity.

Figure 6.4-2. Change in device normal resistance with time during elevated temperature burn-in trials. The resulting degradation is due to Nb oxidation which would not pose a problem during normal operation and storage of the detectors.

Figure 6.4-3. Picture of the new linear DROID manufactured by Oxford Instruments which is currently undergoing testing. The device also possesses a single pixel to act as a process control, comprised of an Ir TES over-coated by an Au absorber. The on-chip Au bias resistor can also be seen. The position information is derived from the differing rise time information of the pulses at the TESs.

6.5 CCD Detectors for Astronomy

Advanced detectors and associated instrumentation are central to PPARC’s long term technology plan (LTTP) and in the UK, one of the most successful detector developments is that with Marconi Applied Technologies (MAT) into CCDs. At Leicester, our current CCD research is concentrating on measures to adapt the CCD X-ray performance to meet the more demanding needs of future missions.

One of the important aims of our CCD research has been to develop the hard X-ray detection efficiency of the current generation of MOS devices. The XMM/EPIC detectors were launched possessing a depletion depth of 35 microns. Competing detector technologies - the pn-CCD and the fully depleted device from Berkley - are limited to the wafer thickness (300 microns). We have performed an investigation into MAT CCDs and found that the limit to depletion was set by breakdown in internal structures in the device. MAT then produced a new design to enable high voltage bias to be applied, and manufactured detectors using our stock of 8000 Ohms/cm bulk silicon. These CCD62 devices were tested, and in the laboratory exhibit ultra-deep depletion in excess of 220 microns. The efficiency of the new devices is given in Figure 6.5-1, together with that of the EPIC devices, plus a standard, low resistivity device and a 300 micron-thick device for comparison. These new detectors will be particularly applicable in future instruments with effective X-ray optics at the harder energies.

We have continued to investigate the radiation susceptibility of X-ray CCDs for space use. In particular, we have performed an investigation into the effects of soft protons (<0.5 MeV) on the device performance. These soft protons were responsible for the substantial damage experienced in the Chandra detectors following launch. They are of concern since the particles come to rest exactly in the charge transport channel of the CCDs and create up to 10x more damage than penetrating particles, as depicted in Figure 6.5-2. We have developed a combined analytical/Monte-Carlo model of the damage produced by 100-300 keV protons, and have compared the simulated results to those measured from irradiated devices. The model shows excellent agreement with the data and can be used as a design tool for future missions. In addition, we have received our new CCD66 devices and performed X-ray testing. These devices possess the new large-pixels with custom electrode structures which were developed at Leicester using advanced 3-D modelling. The electrode structure is designed for improved radiation hardness. Figure 6.5-3 gives a photomicrograph of the pixel structure of these devices and indicates the charge transport region. These detectors avoid the triple buried-channel implants used in XMM/EPIC to improve radiation hardness, using profiled electrodes to control the charge flow in the device and achieve the same result. This reliance upon design rather than fabrication for performance results in a higher yield process. These devices should possess a three times improvement in radiation hardness over the XMM/EPIC CCDs. Tests are currently underway.

We have developed new CCD drive electronics with read noise of 7 electrons rms at 1 MHz (compared to the EPIC specification of 5 electrons rms at 200 kHz). This work is now augmented through a PPARC PIPSS award (starting September 2001) which will develop low-noise analogue ASIC technology. From this will develop a multi-node, high throughput, hybrid demonstrator with one hundred times the X-ray throughput of XMM/EPIC, and suitable for the XEUS mission.

Figure 6.5-1. Comparison of the quantum efficiency for hard X-rays measured for the new ultra-deep depleted CCD62 which was developed on 8000 Ohms/cm bulk silicon. This is compared to that of a standard low-resistivity CCD, the high energy performance of the XMM/EPIC instrument and the limit set for a Si wafer of 300 microns thickness.

Figure 6.5-2. The energy deposited in the active buried channel of the EPIC CCD22 is shown as a function of proton energy. The energy excess indicated by the deviation from the straight line is due to the protons coming to rest in the buried channel itself.

Figure 6.5-3. Photomicrograph of a CCD66, with the new electrode structure designed under this programme. The pixels shown are on a 70 micron pitch using 4-phase electrodes. The charge transfer path and the storage points (arrowheads) are indicated.

ARCHIVES, DATABASES & E-SCIENCE

7.1 Introduction

The Leicester X-ray and observational astronomy group plays a leading role in a number of projects in the e-science area. It provides the Leicester Database and Archive Service (LEDAS), which has been supplying high energy astrophysics-related data to the UK community since 1990, and is seeing downloads at a rate of 18 GB/yr. It is the PI institute in the XMM Science Survey Centre, responsible for science analysis software design and provision, pipeline processing of all the data, and follow-up work to classify the sources seen by XMM. The group is also a leading member of the AstroGrid consortium, which was recently given the go-ahead to provide substantially improved accessibility to, and interoperability between, the very large datasets soon to become available.

7.2 Leicester Database and Archive Service (LEDAS)

The Leicester Database and Archive Service (LEDAS) at http://ledas-www.star.le.ac.uk/ is an online astronomical database service providing access to catalogues and data product archives with an emphasis towards high-energy astrophysics. The service originated in 1990 as a mirror of the Exosat database system based at ESA/ESTEC and NASA/GSFC, and has since grown to the point where it now offers immediate access to online archives from most major X-ray satellites, images from the Digital Sky Survey, and data from many astronomical catalogues. The LEDAS cluster now stores 540 GB of catalogue and archive data on magnetic disk, with the data volume growing at over 200 GB/year.

The most popular method of accessing LEDAS is via the web-based system ARNIE. This service integrates catalogue and archive searching into a single intuitive visual interface. For those who prefer a command-line interface, searches can be performed via telnet to a captive account that gives access to the BROWSE database management system.

LEDAS issues regular news updates via the Starlink News system, by email newsletters to a mailing list of 250 recipients, and the LEDAS staff also make presentations at National Astronomy Meetings.

7.2.1 LEDAS III developments

7.2.1.1 Chandra archive

LEDAS provides a UK mirror of the Chandra science website (at http://ledas-cxc.star.le.ac.uk), including news, up-to-date observing information, proposal tools, documentation and data reduction software. From Nov 2000, LEDAS has also been the host to the only mirror outside the United States of the Chandra data archive. We provide fast access for UK users to download raw and processed public-domain Chandra data via a simple web interface. The archive currently stores more than 220 GB of data, an amount increasing by 190 GB per year.

7.2.1.2 Software development

Development of the software underlying the LEDAS archives is continuing. The newest search facility currently available at LEDAS is BLASTA, a fast web search interface for large astronomical catalogues. BLASTA is based on the WCSTools software created by Doug Mink of CfA, and can handle searches on databases up to 10's of GB in size.

ARNIE5, the next generation of the ARNIE web interface, will use an open-source DBMS (MySQL) and the latest web-programming techniques to provide an enhanced service. ARNIE5's features will include the ability to synchronise automatically with new data holdings at HEASARC/GSFC, search across multiple catalogues simultaneously and output results in a wide variety of formats.

The range of catalogues available to LEDAS users will soon be greatly expanded with the debut of a local web interface to the ViZieR archives at CDS Strasbourg. ViZieR holds approximately 3,300 catalogues and datasets from the astronomical literature. LEDAS has also recently added a convenient bibliographic search facility linked to the CDS.

7.2.1.3 Hardware development

The past two years have seen a great deal of hardware and software development to support enhanced operations at LEDAS. A DEC AlphaServer 1200 currently provides the majority of LEDAS web and archive services. The capacity of its disk array has been expanded to a total of 630 GB to accommodate the growth in the archives. LEDAS has also purchased a powerful Linux PC with 100 GB of disk capacity to serve new large catalogues such as 2MASS. A new Windows-NT machine running commercial software aids the design and maintenance of the website. Data backups are now completely automated, and handled by a 1 TB Exabyte tape library.

The provision of the Chandra archive has involved the installation at Leicester of a high-performance Sun E-250 database server with Sybase DBMS and a 625 GB RAID array, while the Chandra web service is provided by a Sun Ultra 5. Upgrade of the web server (to an Ultra-80 server) to support the new Java-based archive interface will occur shortly.

7.2.2 Other LEDAS services

7.2.2.1 ROSAT/ASCA/Ginga archives

Calibrated public data products, e.g. images, spectra and light curves from ASCA, Ginga and ROSAT are available for download from LEDAS where the data are stored on RAID magnetic disk for fast and reliable access. Recent additions have included the Rosat All-Sky Survey and Rosat HRI pointed results datasets; ASCA data continues to be ingested as the final observations become public.

The archive web interface now automatically generates image previews to allow rapid selection of the desired data.

7.2.2.2 ARNIE/Catalogue holdings

ARNIE (ARchive Network InterfacE) provides a web-search interface to over 200 astronomical catalogues, including sky surveys at several wavelengths, X-ray plasma physics data and X-ray satellite observing logs; it also provides the most convenient route to the bulk archive datasets. The ARNIE catalogues can now be accessed directly from the STARLINK viewer GAIA, and source positions overlaid on sky images.

7.2.2.3 BLASTA/Large catalogue access

BLASTA is a companion search engine to ARNIE for large catalogues, providing enhanced output options. BLASTA currently serves 4 large catalogues (USNO, GSC, ACT, Tycho), but its high efficiency will become essential with the inclusion of the 2MASS catalogue (162 million objects).

7.2.2.4 Digitised Sky Survey

Users can access the Digitised Sky Survey via a fast web interface, which provides images of the selected region of sky in GIF, FITS or HDS format. The pixel scale and image size (up to 1.5 degrees) are user-selectable, and users can now request several images simultaneously using a batch interface. The response speed of the service has recently been improved by a factor of 3 by moving to a more modern server.

7.2.2.5 Software provision

LEDAS mirrors the HEAsoft (ftools, xanadu) and PIMMS software distributions from HEASARC/GSFC. The ftools package provides FITS file utilities and instrument-specific analysis tools. PIMMS converts X-ray count rates and fluxes from one system to another. On-line access is also available through the W3PIMMS web service at LEDAS.

LEDAS also mirrors the Chandra data reduction software suite CIAO. The CIAO software package is several hundred MB in size, too large to be easily downloaded from the US.

Figure 7.2-1. Monthly access statistics for the two major LEDAS services: the LEDAS web and the Chandra web mirror. Whole page downloads per month, robots excluded

Figure 7.2-2. Current LEDAS main bulk data holdings

Figure 7.2-3. Recent LEDAS bulk data download rates per month (excluding web pages)

7.2.3 LEDAS usage statistics

LEDAS web accesses have continued to climb since 1999, showing the ongoing popularity of the service. Page views on the main LEDAS webserver LEDAS-WWW have increased from 13,000 to c.20,000 per month over May 1999 to April 2001 (after filtering for web robots). Accesses to the Chandra web mirror LEDAS-CXC have increased from zero to ~3,000 page views per month over the same period. Over the past year, we have been providing total data downloads of typically 18 GB per year.

7.2.4 Future vision

LEDAS will be submitting a proposal for a renewal of its funding in late 2001 to support continued operation of the Chandra mirror and all other archive systems, and also to provide new datasets (eg RXTE, DSS II) and prepare for new relationships with XMM data and the AstroGrid project.

7.3 XMM-Newton Survey Science Centre

7.3.1 Introduction

The XMM-Newton Survey Science Centre (SSC), led by Leicester, is an international collaboration involving a consortium of 9 institutions in the UK, France, Germany and Spain, together with 6 Associate Scientists. The SSC, which was set-up in 1996 after selection of the consortium by ESA, has a broad role in the XMM-Newton project.

The main responsibilities of the SSC are:

• A major contribution to the development of the scientific processing and analysis software for XMM-Newton

• The routine "pipeline" processing of all the observations

• The compilation of the XMM-Newton Serendipitous Source Catalogue

• Coordinating a follow-up and identification programme for XMM-Newton serendipitous sources

7.3.2 Scientific software development

Since 1996 the SSC has been working closely with ESA's Science Operations Centre (SOC) staff in the development of the scientific analysis software required for the XMM-Newton project: the `SAS' (see Figure 7.3-1). This is the software that both carries out the initial pre-processing of the XMM-Newton scientific data and permits the detailed scientific analysis of the observations: the modules can be used in a fixed configuration for the routine processing of the XMM-Newton data, and can be used in an interactive configuration by XMM-Newton observers to carry out custom analysis of their data. The SSC's contribution to the SAS has been large with the SSC providing essentially all the software required for the processing and analysis of the data from the EPIC X-ray cameras and the Optical Monitor, as well as a significant fraction of the RGS software. Leicester efforts have focused on the overall management and coordination of the SAS development task as well as the provision of a fraction of the SAS software itself.

SAS 5.0, the first public version of the SAS was released in Dec.2000. SAS developments and improvements are still continuing, driven primarily by experience gained with the processing and analysis of real XMM-Newton data. At the time of writing, version 5.1 of the SAS is undergoing final testing with a planned release in June 2001.

Figure 7.3-1. An overview of the current XMM SSC processing pipeline.

7.3.3 Pipe-line processing and the Serendipitous Source Catalogue

In parallel with the software developments, the SSC has developed the infrastructure required to carry out, on behalf of ESA, the routine "pipeline" processing of all the XMM-Newton observations from each of the three instruments. The aim here is to provide a set of data products which will be of immediate value for the XMM-Newton observer as well as for the science archive where they will also be stored for eventual public release. The XMM-Newton data products include calibrated, "cleaned" event lists which are intended to provide the starting point for most interactive analysis of the data as well as a number of secondary high-level products such as sky images, source lists, cross-correlations with archival catalogues, source spectra and time series. These provide a useful overview of the observation for the XMM-Newton observer as well as constituting key archival resources and the starting point for the compilation of the Serendipitous Source Catalogue.

Leicester hosts the pipeline processing system, and has the primary responsibility within the consortium for the design, implementation and operation of the pipeline. Problems within ESA's SOC meant that XMM-Newton datasets in the correct `ODF' format were not produced until mid-October 2000. This led to delays to the testing and final implementation of the pipeline system. Nevertheless the first datasets were pipeline processed in December 2000 and the pipeline operations have been routine since early 2001, although significant enhancements to the pipeline and the component SAS tasks are continuing. ESA commenced the distribution of the ODFs and associated pipeline datasets produced by the SSC to observers in February 2001.

Following on from pipeline processing, the SSC also has the responsibility for producing a catalogue of the serendipitous X-ray sources detected by XMM-Newton. The XMM-Newton Serendipitous Source Catalogue will be based on the EPIC source lists from the processing, but will also contain comprehensive archival catalogue data, and results from the SSC (and other) follow-up programmes described below. Compilation of the catalogue will start later this year. It is planned that the catalogue will emphasize reliability, uniformity and usability as well as paying particular attention to the external catalogue correlations and identification information. The provision of ancillary information such as sky-coverage and sensitivity estimates will ensure the scientific usefulness of the catalogue.

7.3.4 The SSC Follow-up and identification programme

The high throughput, large field of view and good imaging capabilities of XMM-Newton mean that it detects significant numbers of serendipitous X-ray sources in each pointing, as is illustrated in Figure.2.9-3. Around 50-100 sources are detected in a typical EPIC field (over the whole field, i.e. in a sky area ~ 0.2 sq.deg.). With the current operational efficiency, XMM-Newton makes of the order 500-800 observations per year, covering ~100 sq.deg of the sky. The XMM-Newton serendipitous X-ray catalogue is thus growing at a rate of ~50000 sources per year.

7.4 Development of new infrastructure software - FIBRE

Excellent progress was made on the development of an astronomically oriented database manager based on FITS tables. The web-based version, FIBRE, has been available for several months to the XMM-Newton Survey Science Centre team as a way of browsing the extensive data holdings. A portable version of FIBRE has also been integrated into the original XMM common data model (CDM) in collaboration with the XMM team at the Observatoire Astronomique de Strasbourg. Some additional security measures had to be devised to allow proprietary data to be handled safely in a package with a public web interface. The combination of the CDM and FIBRE supports the original database schema, but allows all the files to be browsed easily, not just the subset imported into O2. However software support for O2 is expected to cease at the end of the year, so further work is needed to support some functions currently handled by O2. In order to overcome the limited speed and functionality of the web interface, an alternative graphical user interface, written in Python using the pCFITSIO and wxWindows packages, is under consideration.

7.5 AstroGrid/E-science

Early in 2000 we became involved in informal discussions with colleagues involved in wide-field astronomy and in the provision of astronomical databases in the Universities of Cambridge and Edinburgh. Our experience in using relational databases within LEDAS, in using an object-oriented DBMS within the XMM-Newton Survey Science Centre, and in handling FITS files (as described in section 7.4 above), all fed into these discussions. The outcome was the development of the AstroGrid Project with the aim of federating our astronomical databases and, in conjunction with similar activities abroad, to work towards the global Virtual Observatory. Since our plans and objectives seemed highly congruent with the Government's plans for e-science, a consortium was formed with additional partners (Jodrell Bank, MSSL, QUB, and RAL), and a formal proposal was made to the PPARC Grid Steering Committee in 2001. The AstroGrid Project has now been approved in principle, with funding for Phase A now agreed. Leicester will be leading work on database management, and on the federation of high-energy data archives.

FACILITIES AND SUPPORTING TECHNOLOGY

8.1 Starlink and Data Analysis Computing

T. Goodwin,C. Page, D. Norris, M. Wace

The Starlink system provides the core data analysis facilities for the X-ray and Observational Astronomy Group. It is shared with the Theoretical Astrophysics Group, which uses around 20% of the capacity. Many users in the Space Research Centre also have accounts for e-mail. We have been able to provide all those active in astronomical data analysis a PC running Linux, mostly less than four years old, which allowed us to retire most of the X-terminals. A dual-Pentium server with redundant discs was purchased in 2001 May to act as file server for the PC collection. Although most Unix software now runs on Linux, there are a few packages for which Sparc/Solaris is still needed. The XMM-Newton Science Analysis Software (SAS) is especially important, but it was developed on Solaris, and release of the Linux version is not guaranteed to the same level of functionality. To support the XMM SAS we purchased the most powerful Sparc-server we could afford early in 2000: a 4-processor E420R, but it is by now often heavily oversubscribed. Our Sparc-server 20/514, purchased in 1994, soldiers on as the main disc and web-server, but needs to be retired soon as it is becoming a maintenance liability.

We also have two Compaq Alpha XP1000s running Tru64 Unix (purchased on University funds) which mainly support stellar atmosphere modelling. Recent tests suggest that while the Alphas still have a speed advantage on computations of this type, x86/Linux machines are now so much cheaper that we expect modelling work to migrate to Linux as well, when the Alphas reach retiring age.

The use of large-format CCDs in optical and X-ray telescopes has greatly increased the disc space users need. Fortunately discs continue to get cheaper, and we now purchase PCs with around 20 GB. There are also many SCSI discs of various capacities on the file servers, totalling around 370 GB. Given the number of discs in use, occasional failures are inevitable. Fault-tolerant RAID systems are becoming more affordable, but our funds have not yet allowed us to purchase one.

Providing an adequate tape backup facility has also been difficult, as tape capacities have fallen behind, and we now use two auto-changers (one using DLT, one Exabyte tapes). We also installed 100 Mb/s Ethernet switches as the network had become a limiting factor. An upgrade to this system will be needed to cope with any additional disc space.

We have three mono and one colour printer which have provided reasonable service, but are starting to need attention as they get near the end of their designed lifetimes.

The University Computer Centre continues to provide good support for networking. The connection to Super-Janet-4 (via the Midlands Metropolitan Area Network) was recently upgraded to 100 megabits/sec, which seems adequate for the immediate future.

The rest of the world has become so much dependent on the software of Microsoft, that e-mails with Word or Excel documents attached have become commonplace. There is also a continuing demand for access to Powerpoint and other PC packages. We have found a reasonably satisfactory solution to these problems by purchasing, on University funds, a PC server and licences for Citrix software, so that Unix and Linux users have full access to Microsoft applications. This service has been very popular, and some upgrade is likely to be needed by 2003.

We have been fortunate in retaining our Starlink Manager, Tim Goodwin, throughout the reporting period. He is assisted by Daniel Norris, as computer operator.

8.2 Mission Design, Engineering and Project Services

The design and development (D&D) of laboratory and space hardware is a very necessary part of the Leicester programme. The widespread use of sophisticated design tools has enabled greater confidence in the ability of the finished product to meet requirements, and our collaborators and project partners increasingly expect us to have used these tools to improve the hardware and software we deliver. In order to respond to these pressures, the engineering group has begun to acquire advanced tools and to introduce expertise by recruitment and to generate skills by training. Meanwhile, the best traditional practices remain in place, and improved product assurance techniques continue to be assessed and adopted where appropriate.

The major change has been in the area of mechanical design and development, where increasing use is being made of a Computer Aided Engineering (CAE) software suite, I-DEAS, running on the Silicon Graphics machine funded by a successful JREI bid. I-DEAS provides drafting, 3-D modelling and finite-element analysis (thermal and structural) for parts, assemblies, mechanisms and harnesses. It also provides project based collaborative data management functions. Furthermore, it provides a complete path from initial design capture to the generation of manufacturing data. Much use is made of the various elements of I-DEAS, and a concerted effort is being made to continuously increase that usage with the ultimate objective of streamlining the D&D process. This streamlining, and its concomitant increase in efficiency, will only come through the training programme already underway.

Mechanical parts manufacturing for laboratory programmes and flight projects has been carried out by a mixture of in-house (both SRC and Physics and Astronomy workshops) and commercial procurement. This mixture has been determined by available capacity, and to a limited extent, the need for certain manufacturing technologies not available in-house. There continues to be a strong preference for the principle of in-house manufacturing for the traditional reasons of ready communication of modifications, and familiarity of requirements. Assembly, most importantly of flight hardware, is entirely done by SRC staff.

Electronics production, save for complex printed circuit board manufacture, is carried out entirely by SRC staff. Facilities for this production have generally kept pace with best industrial practice, but there is scope and a plan for improvement and integration with the design process through CAE as is being done on the mechanical side.

The complement of staff of the engineering group is presently 23, including software engineers. The group is responsible for the design, development, manufacturing, testing and sustaining engineering for the laboratory facilities, experiment hardware and software, and flight instrument hardware/software described elsewhere in this report. Additionally they contribute to the support of research programmes.

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