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X-ray and Observational Astronomy
Group |
Julian Osborne : Data Analysis & Data Archives
In the last few years I have been leading a team of astronomers and engineers at Leicester to fulfil our obligations to the Swift project. Before that, my main role was to provide direction for the XMM-Newton Science Analysis Software
provided by the Survey Science Centre. In addition I am the
LEDAS data archive manager.
Swift post-launch support
Swift is a US/UK/Italian satellite
designed to study gamma-ray bursts. Launched on November 20, 2004, it includes a wide area Burst Alert Telescope and narrow field X-ray and UV/optical telescopes. The Swift satellite is unique in that it can
autonomously detect gamma ray bursts and re-point within a few
seconds, so catching them when they are still bright.
Swift has been making detailed observations of around 100 GRBs a year, getting lightcurves and spectra from the time of the burst to up to a hundred days after. A gamma-ray burst signals the creation of a black hole, and GRB research has been at the forefront of high energy astrophysics since this was realised in the late 1990's.
Swift is partly a 'spare parts' satellite, having been made
cheaply from left-over bits from earlier projects. Examples of this
include two major parts of the X-ray telescope: the X-ray CCD in the Leicester-supplied X-ray camera (which is a duplicate of an
XMM EPIC MOS CCD), and the X-ray mirrors, which are from the Italian Jet-X project (see these pictures); and the
UV/optical
telescope, which is also a near XMM duplicate.
Leicester has also supplied
the optical XRT telescope alignment monitor, designed to ensure that the GRB
X-ray positions promptly distributed have the best possible positional accuracy.
Leicester has naturally played a significant role in calibrating the XRT,
and this continues in orbit; Leicester scientists continue to enhance the so-called 'response matrix', which describes the spectral response of the CCD to the incoming X-rays. Leicester also hosts the UK Swift Science Data
Centre, providing
fast and easy access for UK astronomers to the rapidly evolving
data, as well as Swift data analysis training for anyone who wants it, and software services to the Swift project.
The XMM-Newton Survey Science Centre
XMM-Newton is the European Space
Agency's X-ray observatory. It has X-ray cameras built by us in
Leicester. Our group also leads the Survey Science Centre of
which I am a member. The XMM-Newton observatory has the largest set
of X-ray telescopes ever, providing good quality images over a
large area with high spectral resolution; it also has co-aligned
X-ray grating spectrometers and and optical/UV telescope. It is
complementary to NASA's
Chandra
X-ray observatory, which provides higher resolution images but
with smaller telescopes.
The SSC is a consortium of 9 European institutes which have the
following jobs:
- Providing software for the scientific analysis of the
data. The SSC provides the instrument-specific software
packages, as well as packages for image creation and display,
source detection, light curve and spectrum creation and display.
ESA's Science Operations
Centre provide infrastructure, interactive and some grating
packages. The entire software set is known as the SAS.
Files are output in FITS format for use with common public-domain
analysis packages.
- Performing the complete processing of the science
data. We have provided a pipeline
processing system which automatically processes all the science
exposures of an observation when it is delivered to us from the
Science Operations Centre. The results of this processing are
manually checked, and then returned to the SOC for distribution to the person
who proposed the observation. This process
typically takes around one week at the SSC. Keeping the pipeline up to date
and free of bugs is a major task. A major effort has been the
first and second XMM catalogues, released in April 2003 and July 2006.
- Characterising of the celestial content of that
data. The X-ray
Identification Programme collects multi-colour optical imaging
for most XMM-Newton fields, together with spectroscopy of selected
objects. These data will allow a statistical classification of the
majority of the X-ray sources detected by XMM-Newton.
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The Leicester Data Archive Service: LEDAS
LEDAS provides an
on-line astronomical database and archive access service for data
from high energy astrophysics missions. LEDAS gives instant access
to almost 1 Terabyte of data through its comprehensive web-based
database query interface. The four main high energy data holdings
are:
- A mirror of the Chandra Science Data
Archive based at the Chandra X-ray Observatory Center (CXC) in
Harvard, USA. Chandra data first began to flow into the public
domain in autumn 2000, and the LEDAS holdings of Chandra public
data are now typically updated every two weeks as the mission
progresses.
- The ASCA Public Data
Archive, released in November 1998 is also available. It provides
access to ASCA images and data files and is a mirror of the
ASCA archive held by HEASARC at GSFC, in the USA.
- ROSAT was
the most successful X-ray astronomy mission to date, completing
nearly a decade of successful in-orbit operations. The UK ROSAT
Public Data Archive contains all public data from the X-ray
telescope obtained during the pointed observation phase of the
mission. ROSAT operations ceased on February 12 1999. The LEDAS
also archives and provides access to XUV Wide Field Camera data
from the All-sky Survey and pointed phases of the mission.
- The Ginga Data
Products Archive was conceived and created by the Ginga
support staff at Leicester. Users of the Ginga archive can
obtain reduced, quality controlled data products (data cubes, light
curves and spectra), thereby making Ginga data more
accessible to the typical astronomer. The archive was completed and
released in January 1998.
In addition to these, the LEDAS also provides access to hundreds of
other astronomical catalogues from ground-based observations and
other space missions. All catalogue and bulk data databases can be
accessed via the web using the ARchive
Network InterfacE (ARNIE).
One of the most important of these catalogues is the 2XMMp catalogue, which provides X-ray measurements on around 123,000 different X-ray sources and products on the brightest of these.
Since May 1998 the LEDAS has offered an optical sky image
creation service, the Digitized Sky Survey
(DSS) Image Browser. The DSS is a digitised version of Schmidt
survey plates covering the entire sky at 1.7 arcsec resolution. The
LEDAS DSS service offers access to the full sky, and users are able
to request images up to 1 degree square in FITS, HDS and GIF
formats (images larger than 1 degree square are also available on
request).
LEDAS provides software for the
analysis of Ginga data, and mirrors the Chandra, HEAsoft (ftools,
fitsio, xanadu and xstar) and PIMMS distribution packages. It also
provides and on-line service to WebPIMMS
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Julian Osborne: 21-Nov-2006
