UCL Department of Space and Climate Physics


Data Selection

The XMM-OM SUSS2 catalogue is populated with 4,008,897 sources from 6604 observations between March 11, 2000 and January 16, 2013. This is not a complete sample because a fraction of observations were removed during data screening. We list the screening criteria below.

Instrument Mode

Only observations taken in imaging mode are included in the catalogue. Fast mode data, which localizes individual photons within a central 22x23 pixel window, are excluded because of the small window size. Similarly, 2x2 arcmin2 high-resolution central windows of the Rudi-5 default configuration are ignored, though note that in the Rudi-5 observations, the central region is also recorded as an 8x8 arcmin2 low-resolution image which is included within the catalogue sample. Observations with the White filter and the Optical and UV grisms are excluded.

Astrometric Correction

The accuracy of XMM-Newton pointing is good to 1.81 arcsec (RMS). Boresight positions of each field are corrected by comparison of XMM-OM sources with the USNO-B1.0 catalogue, although a minimum number of source detections are required to perform the correction accurately. Only sources from images meeting the following criteria are included within the catalogue:

There are > 4 source detections.

The RMS residual between matched source positions and their USNO-B counterparts < 1.5 arcsec.

The 1σ error in the computed boresight correction < 1.0 arcsec in both the Right Ascension and Declination directions.

Crowded Fields

Both the source detection algorithm and aperture photometry become increasingly uncertain in crowded fields due to source confusion and lack of background measures. Fewer fields have been excluded for this reason in this version of the catalogue than the first version. 

Known issues

Some other specific observations are excluded because they have problems described in the known issues section.