### TGS responses problem

The TGS response originally generated at the EXOSAT observatory were in the
old SF format. At HEASARC the responses were translated into a FITS format
using the program rsp2rmf.

A peculiarity of the grating response is that different orders can overlap in
channel space. Therefore at given energy range, the total efficiency in one
channel is the sum of the effiencies of all left and right orders which
contribute to that channel. The original TGS responses were written such that
at given energy range, the efficiencies which contribute to a channel range
for each order were kept in separate group. Therefore several groups could
overlap in channel space when several left and right orders contribute
to the same channel.

The program rsp2rmf assumes that at given energy range each group
contributes to a unique channel range and does not account for several
groups contributing to the same channel space.
The resulting TGS response matrix has therefore a deficency in the total
efficiency at energy where several left and right orders overlapped.
The wrong version of these FITS matrices were in the HEASARC archive
since March 1995, and distributed on the CD 'Spectra and Lightcurves'
(June 1996).

The faulty responses were remade using a modified version of rsp2rmf.
Two sets of FITS response matrices were remade. The first set preserves the
structure that was in the original format, that is for a given energy
range, the efficiencies for each order (either with the left and right
separated or summed) which contribute to a channel range are kept in separate
group (ORDERS SEPARATED). The second set, for a given energy range, has
summed together the efficiencies for all orders which contribute to
each channel (ORDERS SUMMED).

XSPEC works correctly on both sets of matrices. All the other programs
which manipulate response matrices (addrmf,dmprmf,marfrmf,rbnrmf)
work currectly only on the second set of files.

In the archive the new responses can be found in the following directories:
/exosat/data/tgs/spectra contain the ORDERS SEPARATED FITS file
/exosat/cdrom/vol2/disc2/TGS contain the ORDERS SEPARATED FITS file
in each subdirectory
/exosat/data/tgs/responses see below

The "/exosat/data/tgs/responses" directory contain:
/tgs responce matrices with the ORDERS SEPARATED
but all the LEFT order are summed to the RIGHT orders.
These matrices are appropriate for the spectra attached
to the database TGS.
/tgs2 responce matrices with the ORDERS SEPARATED
The LEFT and the RIGHT order are not summed.
These matrices are appropriate for the spectra attached
to the database TGS2
/tgs_sum responce matrices with the ORDERS SUMMED
but all the LEFT order are summed to the RIGHT orders.
These matrices are appropriate for the spectra attached
to the database TGS.
/tgs2_sum responce matrices with the ORDERS SUMMED
The LEFT and the RIGHT order are not summed.
These matrices are appropriate for the spectra attached
to the database TGS2.
/images image file containing an image of the responce.
/wrong contain the old faulty version of the response files.