The 4XMM-DR9s catalogue of serendipitous sources from overlapping XMM-Newton observations

The stacked catalogue 4XMM-DR9s has been compiled from 1 329 groups, comprising 6 604 overlapping good-quality XMM-Newton observations. They were selected from the public observations taken between 2000 February 3 and 2018 November 13 which overlap by at least one arcminute in radius and are not affected by very high background emission. It contains 288 191 unique sources, 218 283 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. 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. The main catalogue properties are summarised in the table below, the data processing and the stacked source detection are described in the stacked catalogue User Guide. Updates compared to the previous version include a significantly larger sample of observations, event-based astrometric corrections before running source detection, revised background parameters, and manually set flags marking obviously spurious detections.

Users of the catalogue are kindly asked to reference the catalogue release paper by Traulsen et al. 2020, A&A, and Traulsen et al. 2019, A&A, 624, A77 (arXiv:1807.09178) in their publications 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."

The catalogue is available for download as a single file xmmstack_v2.0_4xmmdr9s.fits.gz in FITS format
and browsable via the web-based interfaces

The XSA provides access to the auxiliary data products per source: a broad-band X-ray image, a colour-coded three-band X-ray image, an optical finding chart, and a long-term X-ray light curve.

Please read the Watchouts section before using the catalogues.

The following table gives an overview of the properties of the 4XMM-DR9s stacked catalogue.

Description 4XMM-DR9s 3XMM-DR7s
Number of stacks 1 329 434
Number of observations 6 604 1 789
Time span first to last observation Feb 03, 2000 – Nov 13, 2018 2000 Feb 20 – 2016 Apr 02
Approximate sky coverage 485 sq. deg. 150 sq. deg.
Approximate multiply observed sky area 300 sq. deg. 100 sq. deg.
Total number of sources 288 191 71 951
Sources with several contributing observations 218 283 57 665
Multiply observed sources with flag 0 or 1 191 497 55 450
Multiply observed and manually flagged 19 224
Multiply observed with a total detection likelihood of at least six 181 132 49 935
Multiply observed with a total detection likelihood of at least ten 153 487 42 077
Multiply observed extended sources with flag 0 or 1 9 457 2 648
Multiply observed point sources with VAR_PROB<=1% and flag 0 or 1 20 588 5 358
Multiply observed point sources with VAR_PROB<= 10–5 and flag 0 or 1 7 478 1 839

The catalogue contains a column with links to the IRAP catalogue server summary pages for each 4XMM-DR9 association to a unique source from stacked source detection. In the case of sources with multiple detections, the summary page of the best detection is selected (i.e., the detection with the largest exposure time, summed over all cameras), and the summary page gives cross-links to the other detections.


The User Guide for the 4XMM-DR9 catalogue provides details on how the observations were processed individually.
The User Guide for the 4XMM-DR9s catalogue.

Additional information is given in


The production of the XMM-Newton serendipitous source catalogues is a collaborative project involving the whole XMM-Newton SSC Consortium:

The SSC team are grateful to the XMM-Newton SOC for their support in the catalogue production activities.

The SSC acknowledges the use of the TOPCAT and STILTS software packages (written by Mark Taylor, University of Bristol) in testing the 4XMM-DR9s stacked catalogue.

Last Update: 21-July-2020