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

• XSA at ESA's XMM-Newton SOC
• Browse at HEASARC NASA GSFC
• The IRAP catalogue server at the SSC institute, Institut de Recherche en Astrophysique et Planétologie

Please read the Watchouts section before using the catalogues.

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

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.

Documentation

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 description of the columns in the 3XMM-DR7s catalogue,
• the table of energy bands. The standard energy bands 1–5 are used for the catalogue and combined into the broad 0.2–12.0 keV band, which is labelled band "8" in the other XMM X-ray catalogues.

Credits

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

• Leibniz-Institut für Astrophysik, Potsdam (AIP), Germany
• Institut de Recherche en Astrophysique et Planetologie, Toulouse, France
• University of Leicester, UK
• Instituto de Fisica de Cantabria, Santander, Spain
• Max-Planck Institut für extraterrestrische Physik, Garching, Germany
• Mullard Space Science Laboratory, University College London, UK
• Observatoire Astronomique de Strasbourg, France
• Département d'Astrophysique, CEA/DRF/IRFU, Saclay, France

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.