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

14 CHAPTER 3. BAT OPERATING MODES AND DATA TYPES
dard FTOOLS software for imaging, timing, and spectral analysis in X-ray astronomy. While the
standard pipleline products are ready-made for rapid analysis, the SDC pipeline may not always
be able to use the newest software, and is constrained to produce only a small number of data
files. The BAT team recommends that for serious scientific analysis, users should make their own
custom science products using ‘batgrbproduct’.
Spectra and response matrices have standard extensions, and are suitable for analysis with
XSPEC.
Light curves are uniformly sampled and have multiple energy channels. They can be viewed
easily with the general FITS viewer ‘fv’, but also with other timing analysis software such as
XRONOS (lcurve, powspec, etc.). Multiple channel light curves can be handled in XRONOS using
the “feN” and “leN” energy band options.
Both detector and sky image files are produced. Detector images are processed with BAT
deconvolution software (batfftimage) to produce sky flux images. The first four extensions of each
file are the detector/sky images in each of four standard energy bands. There are also GTI and
EBOUNDS extensions. Following that, there is a BAT DPI TOT/BAT IMAGE TOT extension
which contains the full energy band. All of these images are standard FITS image extensions which
can be viewed with DS9, fv, or your image viewer of choice.
The “pre-slew” sky image (swNNNNNNNNNNNbevps sk.img) has a special BAT CATALOG
as its last extension, which was produced by batcelldetect. The columns RA OBJ,DEC OBJ
of this file represent a fit to the position of the source using all pre-slew data. Because the full
pre-slew burst interval usually contains more data than the BAT on-board trigger interval, this
position will usually be a more precise measure of the source position.
The “GTI” file contains multiple time intervals of interest for a gamma-ray burst, including
T50, T90, T100 (estimated total burst interval), and various background intervals. These intervals
are computed by the battblocks task. They are standard GTIs which can be use for time filtering
of Swift data.
The time intervals identified in the table are defined in the following way:
• pre-burst means before any significant burst emission;
• pre-slew means burst emission before the spacecraft slews to the burst location;
• slew means burst emission during the slew to the burst location;
• post-slew means burst emission after the slew to the burst location;
These intervals are entirely separate from the trigger time calculated by BAT on-board the
spacecraft.
Not all of the data files will be present for every burst. In some cases, the spacecraft does
not slew to the burst, so there may not be slew or post-slew products. Also, occasionally the
battblocks task fails to find sensible time intervals, in which case no standard products will be
present (this most often occurs for faint, short bursts).
3.3 Non-GRB Products
The BAT also generates products that are not associated with a particular gamma-ray burst. These
are typically produced continuously, or at regular intervals in the course of normal operations.