The images below consist of all observations used for the 1XMM catalogue. The number of sources per
image pixel are added up and displayed as intensity. In the left hand panels all sources are
shown. In the middle panel all 'good' sources are shown, that is, all sources where Flag #1 ('False
detection') is not set (=F). The right hand panels show all sources that were
flagged as false (Flag #1 is set to T).
Both the left and right hand images show the problems with false detections in the PN: Apart from
out of time events, the repeated detection of the central source in the adjacent (lower) CCD and the halo of false
detections around the central bright source, there are also a few hot pixels (in the right upper
quadrant, and at the bottom to the left of the center) and a short bright segment (second upper CCD from the
left close to the center line). It becomes clear from the central image that some of the hot pixels
have been missed. On the other hand, the central image shows clearly the random distribution
of all sources (except for the central source which appears in about the same location in most
The persistent false detections in the M1 image are mainly a bright segment at the top of the central
CCD and the corners of the
central CCD and CCD #4 (see also the examples here). Furthermore,
the RGA diffraction spike (the horizontal central line) and, fainter, the out of time events
perpendicular to it in the central CCD are obvious, as well as the halo of spurious detections
around the central source.
The M2 images show a few brighter spots that have not been screened, most of this would be due to
warm pixels which were not meant to be screened. A short segment is obvious at the upper left corner of the
central CCD, though this could be also due to a chance alignment of a couple of warm pixels (nothing
had been obvious here during the screening process). The RGA diffraction spike (only one-sided), out of time events (in
the same direction as the RGA diffraction) and the halo due to spurious detections in the halo of
the central source are also obvious features.