[vsnet-grb-info 6701] GRB 080927: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8302
SUBJECT: GRB 080927: Fermi GBM detection
DATE:    08/09/30 15:04:40 GMT
FROM:    Elisabetta Bissaldi at MPE  <ebs at mpe.mpg.de>

E. Bissaldi, S. McBreen and A. von Kienlin (MPE) 
report on behalf of the Fermi GBM Team: 


"At 11:30:32 UT on 27 September 2008, the Fermi Gamma-ray Burst Monitor
triggered and located GRB 080927 (trigger 244207833 / 080927480).
The on-ground calculated location, using the Fermi GBM
trigger data, is RA = 57.8, Dec = +30.0 
(equivalent to J2000 03h 51m, 30d 00'),  
with a statistical uncertainty of 4.0 degrees (radius, 1-sigma 
containment; there is additionally a systematic error which is 
currently estimated to be 2 to 3 degrees). The angle from the 
Fermi LAT boresight is 75 degrees. 

This GRB is singled peaked with an estimated 
T90 (25-1000 keV) of about 25 s. 
The time-averaged spectrum from T0-1.3s to T0+20.2s is 
adequately fit by a simple power law with index -1.5 +/- 0.1.
An improvement in the fit is obtained using the
Band model with Epeak = 40 +/- 10 keV and beta = -1.7 +/- 0.1.
However alpha is poorly constrained.

The fluence (25-1000 keV) in this time interval from the 
power law model is (5.7 +/- 0.2)E-06 erg/cm2.
The 1s peak photon flux measured starting from T0+5.9 
in the 25-1000 keV band is 2.0 +/- 0.1 ph/s/cm2.


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