The standard spectral file consists of a FITS file with a number of extensions. For imaging detectors the primary array can contain an image of the region from which the spectrum was extracted. Each PHA dataset is contained within a

  • Data Extension
However, each file may also include a number of (optional) associated, additional extensions which contain the detector- and observation-specific information required for construction of the calibration data etc. (i.e. describing how that PHA dataset was selected, housekeeping parameters during the extraction etc. ). These include:
  • a Good Time Interval (GTI) extension
  • a Detector extension
  • a (Selector) History extension
The format of these extensions will also conform to OGIP standards. It should be noted that none of the latter optional extensions are strictly mandatory for specification of the PHA dataset, and hence as an input to XSPEC. Thus these extensions are not discussed in detail here, and if disk space becomes a problem may be deleted by the user prior to using XSPEC. However, it should be stressed that any analysis package may require information in the GTI and Detector extensions when joint spectral/temporal and/or spectral/spatial analysis is to be performed. Information from the Detector extension will also be required when background modelling is to be performed. Such complex, detector-specific tasks will be discussed individually elsewhere. However, in most cases the XFLTXXXX keyword (discussed below) provides an adequate description of the required information.

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Last modified: Thursday, 21-Oct-2021 12:50:38 EDT