User’s Guide – 2.2 Field selection for the catalogue

The catalogue of sources in overlapping observations is based on data used to compile the XMM catalogues from individual EPIC observations and their selection criteria: Observations enter the catalogues, if they have a minimum net exposure time of 1 ks, which is the sum of good-time intervals after filtering the event lists, and non-empty images in all five energy bands. This first release of a stacked catalogue comprised selected good-quality observations. In the following releases, almost all overlapping observations were included:

  • Observations are included if they overlap by at least 1 arcminute in radius,
  • exposures by an instrument are included if the mean background level of each CCD (pn: chip quadrant) lies below the defined thresholds,
  • EPIC/pn exposures in small-window mode are excluded because of their small area,
  • the central CCDs of EPIC/MOS exposures in small-window mode are excluded, while the outer CCDs are included.

The final 4XMM-DR10s sample includes 7 803 observations in 1 396 stacks, the majority of them having two or three members.


Stack sizes in 4XMM-DR10s Multiply observed sky area in 4XMM-DR10s over cumulated exposure time for the three EPIC instruments and their combination
Number of observations in the 4XMM-DR10s stacks. Cumulative sky area of multiply observed 4XMM-DR10s regions over cumulated exposure.

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