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

32 CHAPTER 5. BAT ANALYSIS PROCEDURES
Search in the BAT trend data by month. See /swift/data/trend/YYYY MM/bat/bgainoffs
on the HEASARC FTP site.
You want the next earliest gain/offset map produced before the event data in question. Since
the trend data are not named by time but by observation, this is especially inconvenient. Rather
than searching all the files in the given month, you can narrow your search. In the event file, look
for the LDPGAIN and LDPOFFST keywords,
ftlist sw00145675000bevshsp_uf.evt.gz K | grep LDP | grep Index
which produces the following
LDPGAIN = 171. / LDP Gain Index
LDPOFFST= 478. / LDP Offset Index
These are semi-unique identifiers of which map were used. If you convert these two index values
to hexidecimal, you get gain=0x00ab, offset=0x01de. This tells you which kind of filenames to look
for in the trend data. You would use a wildcard mask like this:
ls sw*bcbo01deg00ab.fits*
Note how the offset index (01de) and gain index (00ab) have been incorporated into the file
name. This command produces the following three files:
sw00067672001bcbo01deg00ab.fits.gz sw00145675000bcbo01deg00ab.fits.gz
sw00145581002bcbo01deg00ab.fits.gz
All of these files should have identical gain/offset contents. However, it is prudent to download
each of them and use the one closest in time to the event data of interest according to its TSTART
keyword.
5.4 Making a Detector Quality Map
Once a BAT event list has been cleaned of diagnostic events and the energy calibration has been
applied, the full detector array should be scanned for anomalous detectors. These are detectors that
have too high or too low counts, compared to the expected statistical distribution. This section
describes how to make a detector quality map, which is used in all following steps, including
performing mask weighting (ray tracing), extracting spectra, light curves, and images.
5.4.1 Reasons to Create a BAT Quality Map
• If it has not been run before (i.e. missing files).
• To capture improvements in the newer software/ground calibration.
• To focus on a narrow energy or time range where some detectors became noisy.