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

60 CHAPTER 6. BAT ANALYSIS ISSUES
The BAT field of view is large, approximately 120 x 60 degrees fully coded. The current
spacecraft constraint excludes the sun with a 45 deg constraint cone, and the earth limb and moon
with 30 degree constraints each.
Even so, the Earth and Moon may enter the BAT field of view. This will most commonly occur
at edges of the “long” BAT axis (i.e. large IMX in the image plane). The effect will be to occult
the flux of sources in that part of the sky. Since the Moon and (primarily) the Earth move as a
function of time, the blockage may have the effect of reducing, but not totally eliminating the
source on-time.
Example: in a 2000 second image, Sco X-1 might be blocked during the final 300 seconds.
The BAT team has released two tools to aid in correcting for occultation.
batoccultmap produces a fractional exposure map for a full sky image. Users provide the sky
image and the prefilter attitude file (“SAO” file), and batoccultmap computes the fractional sky
exposure in each pixel. This task should be used when users are interested many sources at one
time.
NOTE: we suggest to only correct for earth occultation. Correcting for sun/moon occultation
typically does not help, since it changes the image statistics in a non-smooth way.
batoccultgti produces a good time interval file (GTI file) for a known source. Good times
are selected based on being unocculted and/or in a certain position in the field of view. This task
should be used when users are interested in a particular source (i.e. not imaging), and should be
used to filter the input data by time before further analysis.
Updated (15 Oct 2005) - to discuss the new occultation tasks
6.3 Old Issues
6.3.1 Analysis: Users must apply systematic error vector for spectral fitting
Task: Spectral Analysis (batdrmgen and XSPEC)
Version: All versions
What Builds: All builds
Problem: Response matrix contains significant systematic errors
Status: Corrective Procedure (HEASoft 6.0.3)
Updated: 17 Jul 2007
NOTE: This corrective procedure is now fully documented in the BAT manual. Users must
continue to apply the systematic error vector as documented.
The BAT detector response matrix has been significantly improved in the HEASoft 6.0.3 release.
However, significant systematic residuals remain. Users should consult the BAT Calibration Status
section for more discussion of this. To account for the residuals, the BAT team has prepared a
systematic error vector which should be attached to all spectra before analysis in XSPEC.
The BAT team has released a task called batphasyserr which can apply the systematic error
vector to BAT spectra. It works for both type I and type II spectral files, and works for any type
of energy binning.
Most commonly, the task will be invoked in the following way:
batphasyserr spectrum.pha CALDB
where spectrum.pha is the spectrum to be modified (it is modified in place). After using this