HDUVERS = 1.1.0

THIS FORMAT HAS BEEN SUPERCEDED BY HDUVERS = 1.2.0 AND SHOULD NO LONGER BE USED (see Section 2.3)

The following changes were made to reflect recommendations R1, R3, R6, R7 & R8 of the HFWG (see HFWG Recommendations).

The following mandatory keywords have been added

• HDUCLASS = 'OGIP' - indicating the organization which devised the file format in use
• HDUCLAS1 = 'SPECTRUM' - indicating extension contains data relating to a PHA dataset
• HDUVERS = '1.1.0' - indicating the version of the HDUCLAS1 format in use.

The following keywords are mandatory if the channel numbering-scheme for an instrument does NOT start at unity:

• TLMIN$nnn$ - giving the minimum legal value for the values in the column $nnn$ named 'CHANNEL' (ie. the lowest PHA channel possible for the instrument under the current operational mode, irrespective of whether or not that channel is stored as part of the PHA dataset).
• TLMAX$nnn$ - giving the maximum legal value for the values in the column $nnn$ named 'CHANNEL' (ie. the highest PHA channel possible for the instrument under the current operational mode, irrespective of whether or not that channel is stored as part of the PHA dataset).

These keywords are optional for datasets for which the channel numbering scheme starts at channel one (and hence the value of the TLMAX$nnn$ keyword should equal the value of the DETCHANS keyword), but are recommended for clarity.

The following changes have been made to the list of (optional) keywords given by Arnaud et al:

• RA-NOM - is no longer used, but replaced by: RA_OBJ - the Right Ascension of the object (in decimal degrees)
  
• DEC-NOM - is no longer used, but replaced by: DEC_OBJ - the declination of the object (in decimal degrees)
  

The following optional (but strongly suggested) keywords have been added:

• CREATOR - to indicate the name & version number of the s/w task which created the PHA dataset. The suggested format is:
  CREATOR = '{progname} v{i.j.k}'
  where {progname} is the task name, and i.j.k its version number (i, j & k integers; k changing most rapidly).
• HDUCLAS2 - indicating the type of data stored.
  Allowed values are:
  • 'TOTAL' for a gross PHA Spectrum (source + bkgd)
  • 'NET' for a bkgd-subtracted PHA Spectrum
  • 'BKG' for a bkgd PHA Spectrum
• HDUCLAS3 - indicating further details of the type of data stored.
  Allowed values are:
  • 'COUNT' for PHA data stored as counts (rather than count/s)
  • 'RATE' for PHA data stored in count/s
• HDUVERS1 = 1.1.0 will maintain compatibility with older software that looks for HDUVERS1 rather than the correct HDUVERS.

These keywords will be used by downstream software to help locate & understand the origin & content of the dataset. The values also allow a number of checks to be performed by downstream tasks and provide warning messages if it appears that the user is attempting to use the dataset incorrectly (eg attempting to subtract background from a background-subtracted dataset).