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

30 CHAPTER 5. BAT ANALYSIS PROCEDURES
5.2.8 Spectral Fitting
For more tips, warnings and otherinformation on spectral analysis with BAT, please see the BAT
Spectrum and Response section.
5.3 Energy Calibration of Events
BAT events telemetered to the ground have raw pulse heights. Individual detectors have different
energy scales which cannot be combined. Energy calibration of the events is required for any useful
analysis. Typically, the SDC performs the energy calibration in their automatic pipeline. This
section provides information on how to check for the appropriate calibration procedure and to
re-run the calibration when necessary.
The energy scale is based on both an on-board pulser (electronics) calibration, and ground
analysis of the instrument performance (both pre- and post-launch).
5.3.1 Reasons to Re-run the Energy Calibration
• If it has not been run before (i.e. missing gain/offset file or something like that).
• To capture improvements in the newer software/ground calibration (see below).
Checking the event file for the correct ground calibration files
You can check the event file to see if its energy scale was correctly calibrated.
Run the command:
fkeyprint sw00145675000bevshsp_uf.evt.gz GAIN
You should see the following results (among other entries):
GAINAPP = T / Gain correction has been applied
GAINMETH= ’FIXEDDAC’ / Cubic ground gain/offset correction using DAC-b
If these keywords don’t exist, or if GAINAPP is false or GAINMETH is not ‘FIXEDDAC’, then
you should run the energy calibration tool.
5.3.2 Prerequisites
• BAT event data
– either original (in obsid/bat/event/swNNNNNNNNNNNbevshsp uf.evt.gz); or
– cleaned event list (See “Producing a Cleaned Event List”);
BAT gain/offset file (in obsid/bat/hk/swNNNNNNNNNNNbcb*.fits.gz);