DSS keywords

It has been proposed that we use these keywords to store information in our FITS headers about the cuts that have been applied to the data. Here is a description of the DSS keywords prepared by Yasushi Ikebe.

Implementation

A set of classes to manage data cuts has been implemented in the dataSubselector package. These classes are now used by the observationSim and Likelihood packages for managing the data selections. Use of these classes have several consequences:

• Since the cut information is encoded in the DSS FITS header keywords, there is now a mechanism for verifying that the various files used in any given analysis, e.g., event files, maps of live time, Likelihood's exposure maps, have been created assuming a consistent set of data selections. This checking is being performed by the Likelihood applications.

• Likelihood's ROI xml file will go away in the version v6, replaced by the DSS header keywords. This means that a separate event file must be created for each time interval to be analyzed. The current version of Likelihood can be run either way (checking is not done if an ROI file is used.)

• Likelihood requires a specific set of DSS selections for its analysis:
  • exactly one acceptance cone cut
  • exactly one energy range cut
  • any number of time range cuts
  • zero or one GTI cuts

• Other cuts may be applied, but likelihood does not check for them or use them in the analysis, so the user still has to understand the consequences of applying other cuts.

• In obsSim, one can now specify an acceptance cone on the sky for filtering the events that are output to the FT1 file(s). There are now also hidden emin, emax parameters for obsSim, and a GTI extension, comprising the full simulation time, is written to the FT1 file output by obsSim. So if an acceptance cone is specified, these form a complete set of cuts for likelihood.

• If an acceptance cone is not specifed in obsSim, one must use the dataSubselector tool to specify the ROI for likelihood.