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

50 CHAPTER 5. BAT ANALYSIS PROCEDURES
Figure 5.6: Bright point source in a BAT sky image.
5.8.8 Making a Partial Coding Image
As described elsewhere, the BAT has a large field of view with a large variation in sensitivity. The
partial coding map describes the fraction of the detector array which is illuminated by each point
on the sky. To make a partial coding map, issue the following command,
batfftimage infile=flare.dpi outfile=flare.pcodeimg attitude=../../auxil/sw00145675000sat.fits
bkgfile=bkg.dpi detmask=../hk/sw00145675000bcbdq.hk.gz clobber=YES pcodemap=YES
Note that the only change from the previous call is to use the parameter “pcodemap=YES”,
and to change the output file name.
5.9 Detecting Sources in BAT Images
This thread describes how to perform blind source detection in BAT sky images using the ‘batcelldetect’
task. It also describes how to measure the intensities of known sources.
5.9.1 Introduction
BAT sky images are very wide field, covering almost 1/8th of the sky at any one time with at
least some partial coding. BAT images have noise properties which are different than most soft
X-ray images. Mostly importantly, BAT images have a gaussian noise distribution. Furthermore,
the noise level varies throughout the image. Image tools designed for soft X-ray astronomy, like
XIMAGE, are not suited to handle BAT images.
The software task batcelldetect can be used to both detect new sources blindly, and to measure
the intensities of sources at known positions. batcelldetect uses the sliding cell method to measure
the local noise properties everywhere in the image, and to find local excesses. A similar, but simpler
method is used by the BAT on-board computer to locate gamma-ray bursts.
In this section we will discuss two cases: