4XMM-DR13s

The 4XMM-DR13s catalogue of serendipitous sources from overlapping XMM-Newton observations has been compiled from 1 688 groups of 9 796 overlapping XMM-Newton observations. They were taken between 2000 February 1 and 2022 November 29 and overlap by at least one arcminute in radius. The catalogue contains 401 596 unique sources, 310 478 of them multiply observed, with positions and source parameters like fluxes in the XMM-Newton standard energy bands, hardness ratios, quality estimate, and information on inter-observation variability. The parameters are directly derived from the simultaneous fit, and, wherever applicable, additionally calculated for each contributing observation. For lower-quality exposures, not used in source detection to ensure the detection quality, the source parameters are derived from subsequent PSF photometry. The number of parameter measurements (total number of observations of all unique sources) has thus increased to almost 1.7 million. Total fluxes and rates are calculated from the measurements in all contributing images as error-weighted means (formerly: exposure-weighted).
The catalogue aims at exploring the multiply observed sky regions and exploit their survey potential, in particular to study the long-term behaviour of X-ray emitting sources. It thus makes use of the long(er) effective exposure time per sky area and offers the opportunity to investigate flux variability directly through the source detection process