The SWIFT BAT Software Guide Version 6.3 30 ... - HEASARC - Nasa

5.3. ENERGY CALIBRATION OF EVENTS 31
The SDC should be producing a gain/offset file for every observation. If it is not present, then
you must locate the nearest one in time in the trend data in the archive. (see the Swift FTP site
in /swift/data/trend/YYYY MM/bat/bgainoffs).
In this case, let us recompute the energy scale for GRB 050713A (obsid 00145675 000) using
the original event file.
5.3.3 Initial Steps
Change directories to the location of the event data.
cd 00145675000/bat/event
If the event file is compressed, unzip it. The energy calibration task modifies the event file in
place, and gzipped files cannot be modified.
gunzip sw*.evt.gz
5.3.4 Compute Energy Calibration for BAT Events
The energy calibration task for events is called ‘bateconvert’. Here is an example run,
bateconvert infile=sw00145675000bevshsp_uf.evt \
calfile=../hk/sw00145675000bcbo01deg00ab.fits.gz \
residfile=CALDB pulserfile=CALDB fltpulserfile=CALDB \
outfile=NONE calmode=INDEF
• infile is the event file to be calibrated
• calfile is the BAT gain/offset file
• residfile, pulserfile and fltpulserfile are ground-derived calibration files that contain the BAT
energy-to-channel conversion
• outfile=NONE indicates that the operation should be done on the file in-place
• calmode=INDEF means to use the default calibration method
5.3.5 What to do if no gain/offset map is present
Gain/offset maps are produced by the BAT flight software periodically to record the pulse height
scale of the electronics. While the BAT electronics appear to be quite stable, these regular calibration
activities are intended to account for any systematic changes over time. Gain/offset maps
are used to compute calibrated event energies from raw pulse heights during ground processing, as
shown above.
It is important to understand that the calibration activities are not synchronized with the
observing plan. The gain/offset map may have been produced during a previous observation.
Normally the SDC retrieves the proper gain/offset map for GRB data and includes it with the
data set. If there are processing errors, or for non-GRB observations, the gain/offset maps may be
missing. If that is the case, the gain/offset map must be found manually from the trend data.