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ASCA Guest Observer Facility

Fixing the GIS3 Bit Problem

All GIS3 PH data acquired in PH mode between 1994 February 10 and 1994 April 8 suffered from an on-board software related problem. Please find the original announcement from the GIS team for details, and the list of the sequences affected by the problem.

During this period, the three least significant PHA bits were stuck in the pattern 101, resulting in a loss of digital resolution. To repair the damage, the GOF has made available a script called gis3bitfix.e. This script makes a set of reprocessed, fixed GIS3 PH science files which have a maximum of 128 channels, as opposed to 1024.

Please note that the script has already been run on REV1 and later versions of archival data. Users of REV1 and later versions of archival data do not have to worry about fixing this problem. Only thing users have to do is to use correct RMFs (see below).

Which response to use?

After the problem was fixed with gis3bitfix.e, RMFs with 128 channels have to be used corresponding to the 128 channels of the PHA data. The 128 channel RMF is available in the ASCA calibration database (click here to obtain the file). This file, gis3v4_0_128ch.rmf, was made with the ftool rbnrmf with the following command from the 1024 channel RMF gis3v4_0.rmf:
rbnrmf infile=gis3v4_0.rmf nchan=128 cmpmode=linear outfile=gis3v4_0_128ch.rmf
When making an ARF with ascaarf, the 128 channel RMF should be used. Then the ARF will have 128 channels correspondingly.

How to run the script

The script is part of the ftools/xselect release and is invoked simply by typing gis3bitfix.e. If no arguments are given, a help message appears on the screen. The script requires:

  1. A file containing a list of the "damaged" GIS3 event files. The Unix command ls -1 ft*G3* > gis3.lis, for example, will make such a file.

  2. Various calibration files - namely, the telescope definition file, gain history file and attitude file - all of which are distributed to GOs by tape with their data and are available in the Archive. Look in the aux directory.

To run the script, please enter the arguments in the following order:
> gis3bitfix.e evtlist calfile timfile attfile
evtlist = name of file containing a list of event files to be corrected
calfile = name of teldef file       (the gis3_phnew* file)
timfile = name of gain history file (the ft*.ghf     file)
attfile = name of attitude file     (the fa*         file)
The resultant files have the extension .fix appended to the file name. To overwrite the damaged files with the fixed files, run the script again - like this:
> gis3bitfix.e evtlist rename

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This file was last modified on Tuesday, 12-Oct-2021 14:34:41 EDT

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