XMM-Newton Science Analysis System: User Guide

6.2.5 Final combined results

• ommosaic (step 13). In case of multiple OM exposures of the same field, with the same filter, ommosaic is used to combine the corresponding skyimages into a single skyimage. If this task is used for the default image mode, it will combine the windows of the five exposures obtained with the same OM filter into a full field image. Otherwise, skyimages are stacked together. Note that the final image is not corrected for coincidence losses nor for deadtime. The exposure times of the original images composing the mosaic are normalised to 1000 seconds.

• omsrclistcomb (step14). The source lists of the different OSW's of all exposures contained in an observation are combined into one single observation source list file using omsrclistcomb, which is invoked when the analysis of the individual science windows is finished. The input parameter nsigma defines the criteria for the spatial matching of two sources in the merging of the source lists. omsrclistcomb generates a master source list with RA/Dec coordinates, RA/Dec errors and galactic coordinates. The list is sorted into increasing RA order. The significance of detection, the instrumental magnitude and its error, the semi-axis of the source detection ellipse and a set of flags are written in the source list for each filter used in the observation. The colour transformations are applied and the source brightness is also listed in a standard photometric system. AB magnitudes and absolute fluxes are also computed and included in the combined source list.

  As in omatt (step 12) if a catalogue file is provided, then the merged list sources are again cross correlated. This allows to derive a correction for sources detected in the UV filters, which in fields with low number of sources detected fails in the first cross correlation done with omatt.