[vsnet-grb-info 6770] GRB 081007 and GRB 081007B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8369
SUBJECT: GRB 081007 and GRB 081007B: Fermi GBM detection
DATE:    08/10/13 18:18:15 GMT
FROM:    Elisabetta Bissaldi at MPE  <ebs at mpe.mpg.de>

E. Bissaldi, S. McBreen (MPE) and V. Connaughton (UAH) 
report on behalf of the Fermi GBM Team: 


"At 05:21:51 UT on 7 October 2008, the Fermi Gamma-ray Burst Monitor
triggered on a very weak burst GRB 081007B (trigger 245049712/081007224).
The duration of this event is about 0.5 s but due to the lack of counts 
it was not possible to accurately localize it or perform spectral 
analysis. 

121 seconds later, at 05:23:52 UT, Swift/BAT triggered on GRB 081007
(Baumgartner et al., GCN 8330). This event was also detected 
by GBM. The angle from the Fermi LAT boresight to the Swift position 
is 116 degrees. Based on the detector geometry GRB081007 does
not appear to be related to GRB 081007B.

GRB 081007 is single peaked with an estimated T90 (25-900 keV) 
of about 12 s. The time-averaged spectrum from T0+0.6 s to T0+6.8 s 
relative to the Swift trigger is adequately fit by a power law with 
an index of -2.1 +/- 0.1, in agreement with the Swift-BAT refined 
analysis (Markwardt et al., GCN 8338). It can also be fit 
with a power law function with an exponential high energy cutoff.  
The cutoff energy, parameterized as Epeak, is 40 +/- 10 keV.
In this case the power law index is poorly constrained (-1.4 +/- 0.4).

The fluence (25-900 keV) for the power law model is  
(1.2 +/- 0.1)E-06 erg/cm2. 
The 1 sec peak photon flux measured starting from T0+0.9 in 
the 25-900 keV band is 2.2 +/- 0.2 ph/s/cm2.


The spectral analysis results presented above are preliminary;
the final results will be published in the Fermi GBM GRB Catalog."