X-ray and Observational Astronomy

News April 2003: First XMM-Newton catalogue released

Some of the sources detected in the EPIC X-ray images that have gone into the first XMM-Newton catalogue.

The first XMM-Newton catalogue of point sources has just been released, accompanied by a PPARC press release.

1XMM is the first comprehensive catalogue of serendipitous X-ray sources from the European Space Agency's XMM-Newton observatory, and has been constructed by the XMM-Newton Survey Science Centre (SSC) on behalf of ESA. Most (> 80%) of the entries have not previously been reported as X-ray sources. This catalogue is expected to become a significant astronomical resource, as it is the largest catalogue of X-ray sources derived from observations with CCD energy resolution over the full 0.2-12 keV energy band.

The catalogue contains source detections drawn from 585 XMM-Newton EPIC observations made between 2000 March 1 and 2002 May 5; all datasets were publicly available by 2003 January 31 but not all public observations are included in this catalogue. Net exposure times in these observations range from < 1,000 up to ~ 100,000 seconds. The total area of the catalogue fields is ~ 90 square degrees, but taking account of the substantial overlaps between observations, the net sky area covered independently is ~ 50 square degrees. The observations sample, albeit sparsely, most of the sky, with the exception of a 'hole' centred in the Cygnus region caused by spacecraft observing constraints.

The catalogue has been made by reprocessing suitable EPIC data with the most recent software and calibrations available. The processing system used was based on the SSC routine processing pipeline used to produce data products for the observers and the archive, and new versions of the EPIC products (including event lists) are available in association with the catalogue. Considerable effort has been expended to 'calibrate' the catalogue in terms of understanding such issues as errors, biases, sensitivity and sky coverage. Extensive documentation describes the catalogue production, qualities and content.

The catalogue source detection and parametrisation technique is optimised for point-like sources, and has been performed across several photon-energy bands and using data from each of the three EPIC cameras - PN, MOS1, MOS2.

The catalogue content includes the source-detection parameters (likelihood, position coordinates, counts, count rate, flux, hardness ratio, background estimates, errors ...); the results of cross-correlation with a large number of archival catalogues (SIMBAD, NED, USNO, GSC, APM, ROSAT ...); quality 'flags' resulting from visual screening, and 'metadata' relating to the observation.

The catalogue contains 33,026 X-ray source detections with likelihood values > 8 and summary quality flag > 0, together with a further 23,685 detections with lower likelihood values and/or summary quality flag = 0 indicating that the detection may be spurious. The 33,026 X-ray source detections relate to 28,279 unique X-ray sources.

The median flux (in the total photon energy band 0.2-12 keV) of the catalogue sources is ~3x10^-14 erg cm^-2 s; ~ 12% have fluxes below 10^-14 erg cm^-2 s^-1.

The positional accuracy of the catalogue sources is generally ~ 0.5-2 arcsec (68% confidence radius) for detections with likelihood > 8. The flux estimates from the three EPIC cameras are overall in agreement to ~ 2% for on-axis sources, and ~ 6% off-axis.

In association with the catalogue itself, various data products are also available (images, exposure maps, sensitivity maps, extracts from archival catalogues and databases ...).

The catalogue is available in several forms and from several servers:

• the XSA, at ESA's XMM-Newton SOC
• the XCAT-DB, at the SSC institute, OA Strasbourg
• LEDAS, at the SSC institute, University of Leicester
• the SSC Home Page, at the SSC institute, University of Leicester
• Vizier, at CDS Strasbourg

XSA, XCAT-DB and LEDAS provide a Web-based user interface allowing filtering and searching of the catalogue, and links to associated data products. The SSC Home Page, XSA and Vizier allow download of the catalogue file in (binary) FITS and plain ASCII-text form.

A paper describing the catalogue will be submitted to a refereed journal shortly. An earlier paper, presented at the X'02 conference in Santander, describes the catalogue as it was in the late summer of 2002.

Other news items are available here.

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Last updated: 2003 April 07 by Julian Osborne