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Description
The 2XMMi catalogue is the fourth publicly released XMM X-ray source catalogue produced by the XMM Survey Science Centre (SSC) consortium, following the 1XMM (Cat. IX/37, released in April 2003), 2XMMp (July 2006) and 2XMM (Cat. IX/39, August 2007) catalogues: 2XMMp was a preliminary version of 2XMM. 2XMMi is an incremental version of the 2XMM catalogue. The 2XMMi catalogue is about 17% larger than the 2XMM catalogue, which it supersedes, due to the 1-year longer baseline of observations included (it is about 8 times larger than the 1XMM catalogue). As such, it is the largest X-ray source catalogue ever produced, containing more than twice as many discrete sources as either the ROSAT survey or pointed catalogues. 2XMMi complements deeper Chandra and XMM-Newton small area surveys, probing a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie. The 2XMMi catalogue provides a rich resource for generating large, well-defined samples for specific studies, utilizing the fact that X-ray selection is a highly efficient (arguably the most efficient) way of selecting certain types of object, notably active galaxies (AGN), clusters of galaxies, interacting compact binaries and active stellar coronae. The large sky area covered by the serendipitous survey, or equivalently the large size of the catalogue, also means that 2XMMi is a superb resource for exploring the variety of the X-ray source population and identifying rare source types. The production of the 2XMMi catalogue has been undertaken by the XMM-Newton SSC consortium in fulfilment of one of its major responsibilities within the XMM-Newton project. The catalogue production process has been designed to exploit fully the capabilities of the XMM-Newton EPIC cameras and to ensure the integrity and quality of the resultant catalogue through rigorous screening of the data. The predecessor 2XMM catalogue was made from a subset of public observations emerging from a re-processing (in 2006/7) of all XMM observations made prior to that point. The creation of the incremental 2XMMi catalogue has been driven by the desire to make public the additional data from that re-processing that were proprietary at the time of the 2XMM release but which subsequently became public before 01 May 2008. These have been augmented with a further 90 observations that have been processed more recently as part of the routine, day-to-day XMM data processing performed by the SSC, which were also public at 01 May 2008. Together, these amount to 626 additional observations (18%) with respect to 2XMM. With these new data, the sky area covered grows by 19% while the number of detections increases by 17% and the number of unique sources by 15%. A key factor in the decision to make the 2XMMi catalogue is the fact that, effectively, all the new data have been processed with the same science analysis software (SAS), pipeline and calibration as used in the aforementioned re-processing. As such, the products from 2XMM and from the new observations form a set of uniformly processed data. With software and calibration changes now being propagated into the SSC processing pipeline, it was deemed timely to make public the largest available uniform catalogue. The catalogue in its FITS version file (2xmmi.fit) has 246897 entries made of 297 columns; a 'slim' version gathering the 39 most relevant columns for the 191870 unique sources detected, is available as an ascii table or a FITS binary table. In both versions, the columns are fully described in the XMM-Newton User Guide available from: http://xmmssc-www.star.le.ac.uk/Catalogue/UserGuide_xmmcat.html The original names of these columns are included in the "Byte-by-byte Description" below (uppercase names within parentheses) Details about the construction of the catalogue can be found from the XMM-Newton Survey Science Centre (http://xmmssc-www.star.le.ac.uk/)
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