SIS and GIS calibration updates

[Koji Mukai <mukai@carfax.gsfc.nasa.gov>]

* SIS energy resolution update

The SIS team has updated the calibration of the 'non-uniform CTI'
effect, which degrades the SIS energy resolution.  (This is the only
known effect for 1-CCD mode data; the RDD effect probably is more
important in the degradation of 2- and 4-CCD mode data, however.)
Users analyzing recent 1-CCD mode data on bright and/or line-rich objects
are advised to regenerate the rmf file using this new calibration.  See

	http://heasarc.gsfc.nasa.gov/docs/asca/nutci.html

for more details.

* Status of the Latest GIS Gain Determination

As of April 2001, there are about 100 sequences in the current ASCA archives
(revision 2) in which the GIS gain was determined by extrapolation because
the data had been processed before the gain correction parameters were 
determined. Using the latest gis_temp2gain.fits calibration file (version
4.3.24 which covers the period till 2001-4-1), we have reprocessed all the
GIS event files for these sequences.   List of the reprocessed sequences as
well as detailed explanation are found at

The reprocessed GIS event files (both unscreened and screened ones) are 
available from ftp://legacy.gsfc.nasa.gov/asca/data/gis_reprocess_2001-April.
Some of the GIS2 data taken between 1999-10-01 and 2000-04-01 show
noticeable improvement of the absolute energy scale after the reprocessing.
Therefore, for energy sensitive data analysis of these sequences, we recommend 
to use the reprocessed GIS data, instead of those in the archives.

We plan to reprocess all the ASCA data to create a uniform final archive.
However, this will not be started until ongoing efforts to improve GIS and
SIS calibration have concluded.  Therefore, these reprocessed GIS event
files will supersede those in the archive for at least the next ~6 months.