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XTENEWS#4: Updates to XTE PCA response matrices

               Updates to XTE PCA response matrices
XTENEWS#4                                           6th April 1995

  A 'What's New' link has been added to the XTE GOF WWW
homepage. Proposers are encouraged to look at this area regularly to
receive updates on software, response matrices, etc. In an attempt to
keep Email traffic down, this XTENEWS list will henceforth only be
used for major announcements. We remind you that the GOF homepage can
be found at

PIMMS2, PCA responses

  New versions of PIMMS2 and the PCA response matrices are now
available. The changes to each remove some small inconsistencies
between these two methods of calculating expected PCA count rates.

  The 6-channel and 256-channel PCA response matrices have been
modified to bring them into agreement with each other.  These matrices
now use a common offset and energy scale.  Previously, the 256-channel
matrix had channels with a slightly larger width in energy and a
non-zero offset.  It also used a larger, but not unreasonable,
estimate for the PCA effective area.  Deriving counts in the 6
canonical channels (1-13, 14-17, etc.) using the 256-channel matrix
will now give lower total count rate estimates (by about 12%) and
shift counts into the lowest canonical channel.  The new 6-channel
matrix produces the same results as the previous set.  The layer
matrices and all the background files are unchanged and retain their
previous names. PIMMS2 has been updated to reflect this, and also now
includes effective areas for HEAO-1 A4 and Spectrum-X-Gamma SODART.

  The latest PIMMS2 may be obtained from the anonymous ftp account on
legacy.gsfc.nasa.gov in the directory:

The complete set of PCA response matrices and background files are in 

The updated files include the string "950403".  All the files are
included in pcamatrices.tar.

  The HEXTE matrices and PIMMS2 determinations are unaffected.

  A full description of the changes will arrive on the 'What's New'
page shortly.  Descriptions of the changes are also included in the
respective README files located in the ftp area.

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