DOI: 10.5281/zenodo.10875231
title: 4XMM-DR12

description: 4XMM-DR12 is the fourth generation catalogue of serendipitous X-ray sources from the European Space Agency's (ESA) XMM-Newton observatory, and has been created by the XMM-Newton Survey Science Centre (SSC) on behalf of ESA. It is an incremental version of the the 4XMM catalogue and contains 502 more observations and 43855 more detections than the preceding 4XMM-DR11 catalogue, which was made public in August 2021. In addition, we provide spectra and lightcurves for more than 17484 more detections than in 4XMM-DR11.

The catalogue contains source detections drawn from a total of 12712 XMM-Newton EPIC observations made between 2000 February 1 and 2021 December 31; all datasets included were publicly available by 2021 December 31 but not all public observations are included in this catalogue. For net exposure time  ≥  1ksec, the net area of the catalogue fields taking account of the substantial overlaps between observations is ~ 1283 deg2.

4XMM-DR12 contains 939270 X-ray detections above the processing likelihood threshold of 6. These X-ray detections relate to 630347 unique X-ray sources. A significant fraction of sources (123037, 20%) have more than one detection in the catalogue (up to 84 repeat observations in the most extreme case).

The catalogue distinguishes between extended emission and point-like detections. Parameters of detections of extended sources are only reliable up to the maximum extent measure of 80 arcseconds. There are 88169 detections of extended emission, of which 20169 are 'clean' (in the sense that they were not flagged).

Due to intrinsic features of the instrumentation as well as some shortcomings of the source detection process, some detections are considered to be spurious or their parameters are considered to be unreliable. It is recommended to use a detection flag and an observation flag as filters to obtain what can be considered a 'clean' sample. There are 821953 out of 939270 detections that are considered to be clean (i.e., summary flag < 3).

For 336776 detections, EPIC time series and 337058 detections, EPIC spectra were automatically extracted during processing, and a χ2-variability test was applied to the time series. 7697 detections in the catalogue are considered variable, within the timespan of the specific observation, at a probability of 10-5 or less based on the null-hypothesis that the source is constant. Of these, 5789 have a summary flag  < 3.

The median flux (in the total photon-energy band 0.2 - 12 keV) of the catalogue detections is ~ 2.3 × 10-14 erg/cm2/s; in the soft energy band (0.2 - 2 keV) the median flux is ~ 5.2 × 10-15, and in the hard band (2 - 12 keV) it is ~ 1.2 × 10-14. About 23% have fluxes below 1 × 10-14 erg/cm2/s. The flux values from the three EPIC cameras are, overall, in agreement to ~ 10% for most energy bands. The median positional accuracy of the catalogue point source detections is generally < 1.57 arcseconds (with a standard deviation of 1.43).

With 4XMM-DR12, we also release 4XMM-DR12s, a new version of the stacked catalogue built from 9352 4XMM-DR12 overlapping observations. 4XMM-DR12s contains 1620 stacks (or groups). Most of the stacks are composed of 2 observations and the largest has 372. The catalogue contains 386043 sources, of which 298626 have several contributing observations. Stacking observations allows yet fainter sources to be detected in sky regions observed more than once, increasing the number of detections and uncovering long-term variability on repeatedly observed objects. 4XMM-DR12s reaches a median depth of ~2.5E-15 and ~6.8E-15 erg/cm2/s in the soft (0.2-2 keV) and hard (2-12 keV) X-ray band, respectively.