VizieR Online Data Catalog: 4XMM-DR9s serendipitous source catalogue from stacks (Traulsen+, 2020)

The 4XMM-DR9s catalogue has been compiled by the XMM-Newton Survey Science Centre (XMM-SSC) Consortium from simultaneous source detection on overlapping observations. Observations with all filters and suitable camera settings were included. Exposures with a high background were discarded. The high-background thresholds were determined through a statistical analysis of all exposures in each instrument configuration. Positional rectification was applied to the observations before source detection. The catalogue makes use of the longer effective exposure time and this higher sensitivity in repeatedly observed sky areas through stacked source detection to discover new sources, provide better constrained source parameters and unveil long-term brightness variations. It lists 288,191 X-ray sources detected in 1329 stacks with 6604 contributing observations over repeatedly covered 300 square degrees in the sky. 218283 sources were observed several times, where the number of observations of a source ranges from 1 to 40. The catalogue provides 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. In particular, source fluxes were derived for all contributing observations, irrespective of whether the source would be detectable in an individual observation.

Source parameters are given for the three EPIC instruments, abbreviated by PN, M1 (MOS1), and M2 (MOS2), and in the five standard energy bands (1) 0.2-0.5keV, (2) 0.5-1.0keV, (3) 1.0-2.0keV, (4) 2.0-4.5keV, and (5) 4.5-12.0keV. All-EPIC values cover the full energy range 0.2-12.0 keV. Hardness ratios are calculated as (H-S)/(H+S) between energy bands H and S: HR1 between energy bands 2 and 1, HR2 between bands 3 and 2, HR3 between bands 4 and 3, and HR4 between bands 5 and 4, respectively. Coordinate equinox is J2000. Image pixels are binned to a side length of 4arcsec. The minimum detection likelihood to include a source in the catalogue is six in the whole stack or at least one contributing observation.

A full description of the catalogue can be found at https://xmmssc.aip.de/

Users of the catalogue are kindly asked to reference the catalogue paper (Traulsen+ 2020) and to include the following policy statement: "This research has made use of data obtained from the 4XMM XMM-Newton serendipitous stacked source catalogue 4XMM-DR9s compiled by the institutes of the XMM-Newton Survey Science Centre selected by ESA."

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