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

44 CHAPTER 5. BAT ANALYSIS PROCEDURES
5.7.3 Change into Event Directory
Change directories to the location of the event data.
cd 00145675000/bat/event
5.7.4 Make the spectrum
BAT spectra are made with the ‘batbinevt’ task. Here is an example for the flare discussed above:
batbinevt infile=sw00145675000bevshsp_uf.evt.gz outfile=flare.pha outtype=PHA \
timedel=0.0 timebinalg=u tstart=142921843 tstop=142921868 \
energybins=CALDB:80 outunits=RATE \
detmask=../hk/sw00145675000bcbdq.hk.gz clobber=YES
• the outtype=PHA means make a “spectrum” (PHA = pulse height analyzer)
• the timedel=0.00 means accumulate all the data in the specified time range into one spectrum
• the timebinalg=u means make them uniform bins (really “don’t care” in this case)
• the tstart and tstop give the start and stop time of the spectrum as discussed above
• the energybins=CALDB:80 means make a default 80-channel spectrum
• the outunits=RATE makes a rate spectrum, which is usually required since BAT spectra
have fractional counts, which XSPEC does not accept
• the detmask is required to filter out noisy detectors
5.7.5 Apply Corrections to the Spectrum
There are several corrections that need to be applied to a spectrum before it can be fit by XSPEC.
The first correction involves inserting the proper ray-tracing keywords into the file.
Several geometric parameters are required to make an accurate response matrix, such as the
position of the burst in instrument coordinates. Because the spacecraft is often slewing during
the burst, it is not possible to know for sure what those geometric parameters should be until
the desired spectrum has been created. The ‘batupdatephakw’ task does this for you, using the
auxiliary ray-tracing file described above. If the auxiliary raytracing file does not exist in your
observation, then you will have to create it using the Mask-Weighting thread. If you do not apply
this correction, then fluxes may be in error by up to 50%, and power law indices may be off by up
to 0.5.
batupdatephakw flare.pha sw00145675000bevtr.fits.gz
Next, you should apply the BAT-recommended systematic error to your spectrum. The ‘batphasyserr’
task is used to do this, and the error vector is stored in the calibration database.
batphasyserr flare.pha CALDB