GCN Circular 2444

HETE Prompt GRB Spectral Analyses

The HETE team has enhanced its prompt burst analysis software to 
perform automatic spectral analyses of Fregate burst data and then
immediately post the results to the HETE web site:
  
  http://space.mit.edu/HETE/Bursts

This automatic spectral fit is derived from triggered data from the
Fregate instrument for bursts which are localized by the WXM and/or
the SXC.  The process takes roughly five minutes to run, and it begins 
as soon as the full burst data set is received at MIT and the WXM 
localization has been confirmed:  the results for a typical burst 
will be posted between 20 and 90 minutes after the burst, depending 
on the location of HETE in its orbit at the time of the trigger.

At present, a cutoff power law is fit to the data, and the calculated 
values of Epeak, 25-100 keV fluence, and burst duration are posted, 
along with a plot of the spectral fit generated by XSPEC (to allow
the observer the opportunity to check the automated results).  Further 
details and caveats on the method are described at

  http://space.mit.edu/HETE/Bursts/Epeak_explanation.html

The burst web page now also includes a histogram plot of the band C
(30-400 keV) S/N ratio, which we have found to be an excellent means
of identifying true XRFs.

This process was first applied to GRB031026, and the results can be
seen at

  http://space.mit.edu/HETE/Bursts/GRB031026

Further improvements in the prompt data to the web page are being 
implemented and will be announced as they are completed.