UCL Department of Space and Climate Physics


Introduction to XMM-SUSS2

XMM-SUSS2 contains source detections drawn from 6604 XMM-OM observations in up to three UV and three Optical broad-band filters made between 11th March, 2000 and 16th January, 2013. All datasets included are publicly available but note that, due to screening criteria, not all public observations are included in this catalogue. Taking account of substantial overlaps between observations, the net sky area covered independently is 19−105 deg2, depending on filter. The primary content of the catalogue is filter-dependent source positions and magnitudes. The catalogue consists of two tables. The first one contains the sources, with positional and photometric data (count rate, magnitude and flux) and quality flags for each measurement. In the second table we give a summary of the observations from which the sources have been detected and measured (see Description of format of XMM-SUSS2).

Improvements in XMM-SUSS2 over the previous version are:

  • more data, including the period from 2007 to 2013.
  • all observations are included, even those that have only optical data and no UV. (In the previous version an observation required at least one UV-filter detection for inclusion.)
  • source detection is performed on stacked images to obtain detections of fainter sources.
  • improvements in error calculation and flagging.

The XMM-OM SUSS2 catalogue contains  5,595,331 source detections above a signal-to-noise threshold limit of 3-σ which relate to 4,008,879 unique objects of which 692,223 (17.3%)  have multiple entries in the source table, corresponding to different observations. A significant fraction of sources (ranging from 15% in B to 19% in V) are visited more than once per filter during the lifetime of XMM. Consequently, the scope for science based on temporal source variability on timescales of hours to years is broad.

The positional accuracy of the catalogue detections is typically 1.0 arcsec (1σ confidence radius) with a mean positional error of 0.67 arcsec. The mean AB magnitude of the catalogue detections in the three UV bands is 18.97 (UVW2), 19.82 (UVM2) and 20.31 (UVW1). 20% of sources have AB magnitudes fainter than 20.06 (UVW2), 20.90 (UVM2) and 21.36 (UVW1). UVW2, UVM2 and UVW1 refer to the filter bandpasses defined in the Source Properties: Filter Set section. 

The processing used to generate the catalogue is based on the SAS14.0 pipeline developed for the pipeline reduction of all XMM-Newton observations. This version includes a number of significant improvements over the previous data processing system (as used by the SSC in routine processing of XMM-Newton data on behalf of ESA). These improvements include a more robust detection scheme for sources close to the limit of sky background, refined quality flagging and a higher success rate (90%) for refined aspect corrections.