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

Chapter 5
BAT Analysis Procedures
5.1 Introduction
This chapter provides information and recipes regarding the analysis of BAT data. The primary
focus of the information is extracting light curves, spectra and images from the event data associated
with gamma-ray bursts.
In response to a gamma-ray burst, the BAT instrument sends raw event data to the ground.
This event data includes all events from particle background, noisy detectors, and non-imaged Xrays.
The user must take advantage of the coded mask analysis in order to remove the effects of
these nuisance components. The technique described here is known as “mask-weighting,” which is
equivalent to a specialized form of ray-tracing.
It should be noted that event data allows maximum flexibility to analyze the data. For example,
the user can select which time intervals they are interested in, and the desired spectral binning.
(Contrast this with survey data, which has a fixed integration time and energy binning scheme.)
The BAT software and hardware has also been designed to allow the user to extract light curves and
spectra while the spacecraft is slewing. This is important because the Swift spacecraft automatically
slews to most bursts, and a significant fraction of the bursts have prompt emission during the slew.
For most GRB analysis, users should begin with the ‘batgrbproduct’ script. This script, described
in the following sections, performs a standard analysis and makes products that will satisfy
many users.
However, this chapter also describes some of the more fundamental building-block analysis
procedures, including:
• Energy calibration of events
• Making a detector quality map
• Mask Weighting (Ray Tracing) for a known source position
• Extracting a light curve
• Extracting a spectrum
• Correcting the spectrum
• Generating a response matrix
• Making sky images
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