XMM-Newton Science Analysis System: User Guide

6.2.7 Deep detection on mosaiced images

Since SAS v9.0 it is possible to run omdetect on mosaiced images. Invoking omichain with the parameter processmosaicedimages will produce a second detection on mosaiced images (if any). New detected sources will be added to the source list. This is the default in SAS v13.0.

• omdetect (step16). A second detection is done in the mosaiced and stacked images (if any). This produces a new source list.

• ommag (step17). Calibration is applied to the sources of the new list.

• omqualitymap (step18). Quality flags are set for the sources.

• omsrclistcomb (step19). The sources obtained from the mosaiced and stacked images are merged as in step14.

• ommergelists (step20). The new sources detected in the mosaiced and stacked images are added to the original combined list. Existing sources from the first run of omdetect in the original images are not changed.

This deeper detection can be applied manually to co-added or mosaiced images from different observations. Since these new sources are very faint the coincidence loss correction is not applied to them. (See the SAS on-line documentation for further details)

It should be noted that this second detection is performed on sky aligned images. Errors in the alignement of the rotated images and rotation induced noise patterns can lead to spurious detections. All new sources are flagged in the final merged list produced by ommergelists.