Last modified: 17 July 2024

Why is my level 2 event file larger than the one from the pipeline?

If you run acis_process_events on a level 2 event file, you will find that the output file is larger than the input file. This is because the stdlev1 value for the eventdef parameter contains an entry for the PHAS column, which does not exist in the pipeline level 2 file (it is filtered out of the level 1 data products). The column is created by acis_process_events and filled with zeros.

There are three ways to deal with this:

  1. Run acis_process_events with an explicit "level 2" eventdef parameter:

    unix% pset acis_process_events \
  2. Remove the PHAS column a posteriori from the output file:

     unix% dmcopy "acis_new_evt2.fits[cols -phas]" acis_new2_evt2.fits

    where acis_new_evt2.fits is the output of acis_process_events run with eventdef=")stdlev1".

  3. Do nothing. The larger file size will not cause problems in the software (other than increasing runtime in some cases), so it is not required that you do anything about this feature.