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

6.3. OLD ISSUES 63
The BAT software tasks depend on the proper DATE-OBS and DATE-END keywords in order
to access the CALDB system. If these keywords are incorrect, then the tasks will attempt to find
the wrong files in CALDB.
Before the date of XXX the Swift Data Center (SDC) produced some files with the date 2001-
01-01, which causes this CALDB problem. You can check for the problem by running most tasks
with chatter=5. If you see “strtdate=2001-01-01” before the task quits, then you have this problem.
Also, you can run fkeyprint filename DATE-OBS and check for ‘2001-01-01’.
A workaround is to correct the DATE-OBS and DATE-END keywords. You can do this with
the following commands:
fthedit myfile.fits DATE-OBS add value="YYYY-MM-DD"
fthedit myfile.fits DATE-END add value="YYYY-MM-DD"
where YYYY-MM-DD is the proper date of the observation.
This bug was fixed on May 4, 2005 (pipeline processing version 2.1.6). However, the workaround
will still be needed for old data before this date, until the SDC reprocesses it.
6.3.5 batoccultmap: incorrect exposure correction
Task: batoccultmap
Version: v4.1 and earlier
What builds: HEADAS 6.0.5 and earlier
Problem: Incorrect exposure over entire image
Status: Fixed in HEASoft 6.1
Updated: 04 Aug 2006
batoccultmap is used to compute the exposure correction due to occultation by the earth or
other celestial bodies. Typically earth occultation only affects the edges of the image. However,
a bug was found in this task which incorrectly computes the exposure correction over the entire
image.
The error does not always occur. The visible portion of the earth’s limb must be entirely in the
southern celestial hemisphere, the earth must be at the very edge of the image, and the CONTOUR
algorithm must be used. Even then, the behavior is not always predictable.
The result is that the full image has a depressed fractional exposure level. Typically the loss is
a few percent. Based on analysis of BAT data from 2005, 93% of results will be correct, 98% will
be correct to within 2%, and 99.5% will be correct to within 5%. For comparison, relative BAT
fluxes are calibrated to within a few percent at best.
Workarounds:
• Use the IMAGE algorithm of batoccultmap instead of the CONTOUR algorithm
• Take the exposure result, and divide the full image by the central pixel value
This bug was been fixed in HEASoft 6.1 (Swift Build 19).