This page explains the steps required to obtain sky images, spectra and light-curves from BAT event data. Running these scripts will result in a BAT spectrum and response matrix, which can then be used in XSPEC, along with spectra from the XRT and UVOT.
Many of these steps are performed by the pipeline at the SDC, but these individual scripts allow users to perform the data analysis "by hand". This is useful both for understanding what the processing does (rather than accepting the outputs of a "black box") and also if a problem with the pipeline were to develop.
The individual scripts are covered below, with some detail about the input files required for each step in the production of level 2 BAT data. Although the entire set of parameters can be typed directly at the command prompt, the required files do have to be in a specific order, which is not immediately obvious. However, the BAT ones will prompt for the required inputs, which simplifies matters. For example, typing
batbinevt will then prompt for input event file name etc. There are, however, some 'hidden' settings, which will not be prompted for; these can be shown by using the FTOOL command
plist, which will show all the parameters, including the hidden values, given in parentheses (example). The hidden defaults can be overridden in 1 of 3 ways: the new value can be defined on the command line (this is the method which has been used below, when going through the individual scripts), the
pset command can be used or the
par file can be edited. For more details on the
pfiles commands, see the FTOOLS Tutorial.
There are many other BAT tasks which can be used to perform tasks such as
refining the GRB position (
batcelldetect) and cleaning the background
fhelp swift lists and explains these
Note that HEASoft includes a complete GRB processing script, batgrbproduct, which generates all the standard products (images, light-curves and spectra) from the observations automatically. This is the recommended method to analyse BAT data. If time-sliced spectra or different energy bands for the light-curves are required, then the relevant threads listed below can be followed.
If a GRB is detected close to the edge of the BAT field of view (low partial coding fraction), the default processing may not show any counts during this time interval. To work around this, the command
batgrbproduct aperture=CALDB:DETECTION pcodethresh=0.01 imgpcodethresh=0.01 extractor=fextract-events should be run.