UCL Department of Space and Climate Physics


SWIFT Data Selection

Most of the UVOT observations between 2005 and 2010 were used as input data to the catalogue. However, here is a list of data that has NOT been included: 

  • Very short exposures (less than 10s),
  • Exposures taken when the Swift star trackers were not locked, leading to smeared images,
  • Exposures not using the full 17x17 arcmin2 field of view,
  • Observations in the WHITE filter or the grisms,
  • Images where the astrometry or aspect correction has failed (see astrometry correction). 

After processing the following were removed from the final catalogue:

  • Magnitudes, fluxes, quality flags for very high count rate sources, such that counts per frame exceed 0.96. This equates to a raw count rate of > 87 c/s and corrected for coincidence loss, >267 c/s. The parameter SIGNIF is not removed, however if no valid measurements are available for any filter the source is removed entirely from the catalogue.
  • Bit 8 quality flags (meaning the source is in an extended feature) where bit_8_fraction > 35% EXCEPT where there is a large galaxy in the field. This fixes the cases where the detection routine has falsely identified a large extended feature covering most of the image. In these cases the sources are retained, but the flag is removed.
  • Fields where the majority of sources were spurious. In these cases all the sources for that particular filter and obsid have been removed.  This is usually caused by the detection routine finding a lower background value and thus falsely identifying many sources.