2XMM is the second comprehensive catalogue of serendipitous X-ray sources from the European Space Agency's (ESA) XMM-Newton observatory. The catalogue has been constructed by the XMM-Newton Survey Science Centre (SSC) on behalf of ESA.

The 2XMM catalogue is the largest X-ray source catalogue ever produced, containing almost twice as many discrete sources as either the ROSAT survey or pointed catalogues. 2XMM complements deeper Chandra and XMM-Newton small area surveys, probing a much larger sky area. The schematic plot to the right, loosely based on Brandt & Hasinger 2005 (ARA&A 43, 827), shows the 2XMM catalogue in comparison with other X-ray surveys. The 2XMM catalogue provides an effective dataset for generating large, well-defined samples of various types of astrophysical object, notably active galaxies (AGN), clusters of galaxies, interacting compact binaries and active stellar coronae, using the power of X-ray selection. The large sky area covered by the serendipitous survey also means that 2XMM is a rich resource for exploring the variety of the X-ray source populations and identifying rare source types. The catalogue contains source detections drawn from 3491 XMM-Newton EPIC observations made between 2000 February 3 and 2007 March 31; all datasets were publicly available by 2007 May 01 but not all public observations are included in this catalogue. The catalogue contains 246897 X-ray source detections which relate to 191870 unique X-ray sources.

The median flux in the total photon energy band (0.2 - 12 keV) of the catalogue detections is ~ 2.5 × 10^-14 erg cm^-2 s^-1; in the soft energy band (0.2 - 2 keV) the median flux is ~ 5.8 × 10^-15, and in the hard band (2 - 12 keV) it is ~ 1.4 × 10^-14. About 20% of the sources have total fluxes below 1 × 10^-14 erg cm^-2 s^-1.

There are 20837 detections of extended emission in the catalogue. For 38320 detections spectra and time series were automatically extracted during processing, and a χ²-variability test was applied. 2307 detections in the catalogue are considered variable at a probability of 10^-5 based on the null-hypothisis that the source is constant.

Access

The 2XMM catalogue, released on 2007 August 22nd, is available in multiple formats:-

• FITS binary format (gzip 206 MB, MD5: 66a70dd94ac110dc90a21c7ffb3b5d44)
  
• CSV format (gzip 244 MB, MD5: 3c0982c107c1842efb4b330442b441a8).
  
• VOTable format (gzip 249 MB, MD5: 01ed39c58d01aba0336af5819b5db25e)

For convenience here is a file containing a suitable SQL CREATE statement for use with a relational DBMS in order to load the data in CSV format. The CSV file has nulls represented by two successive commas, compatible with Postgres and (probably) other DBMS.

The following Web-based user interfaces will allow filtering and searching of the catalogue

• ARNIE5 at LEDAS, University of Leicester
• XSA at ESA's XMM-Newton SOC
• XCAT-DB at the SSC institute, OA Strasbourg
• Browse or Browse 2XMM at HEASARC NASA GSFC

Documentation

The User Guide for the 2XMM catalogue contains details of the catalogue production process and content. Here are quick links to the description of the columns in the catalogue and the list of observations used to compile the catalogue. Note that modified energy bands have been used for this catalogue (as well as the pre-release catalogue 2XMMp).

Nomenclature and Citation

The correct nomenclature for references to sources in the catalogue is the name starting with the '2XMM' designator, as included in the catalogue itself, followed by a colon and the detection identification number where a specific detection is referred to (rather than the source itself), that is: "2XMM Jhhmmss.sSddmmss:detid".

The production and content of the 2XMM catalogue is described in detail in Watson et al. (2007), "The XMM-Newton serendipitous survey. V. The Second XMM-Newton Serendipitous Source Catalogue," , in preparation.

Credits

The production of the XMM catalogue is a collaborative project involving the whole SSC Consortium:

• University of Leicester, UK
• Mullard Space Science Laboratory, University College London, UK
• Institute of Astronomy, Cambridge, UK
• Max-Planck Institut für extraterrestrische Physik, Germany
• Astrophysikalisches Institut Potsdam, Germany
• Service d'Astrophysique, CEA/DSM/DAPNIA, Saclay, France
• Centre d'Etude Spatiale des Rayonnements, Toulouse, France
• Observatoire Astronomique de Strasbourg, France
• Instituto de Fisica de Cantabria, Santander, Spain
• Osservatorio Astronomico di Brera, Milan, Italy

The SSC team is pleased to acknowledge the contributions to the SAS software, on which the catalogue processing is based, made by ESA's Science Operations Centre staff. Significant contributions to the earlier-mission software and data-processing activities were also made by NASA Goddard Space Flight Centre HEASARC staff resident for a substantial time at the University of Leicester. The quality of the pipeline products and the catalogue itself were ensured by the dedicated and sustained efforts of the screening team: Hermann Brunner (MPE), Marcella Brusa (MPE), Maite Ceballos (IFCA), Stephanie Dupuy (CESR), Sean Farrell (CESR), Federico Fraschetti (CEA), Georg Lamer (AIP), Anja Schroeder (LUX), Mark Simpson (LUX), Giorgia Sironi (OAB, LUX), Ann-Marie Stobbart (LUX).