[vsnet-grb-info 10800] GRB 110731A: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12221
SUBJECT: GRB 110731A: Fermi GBM observation
DATE:    11/08/01 06:29:38 GMT
FROM:    David Gruber at MPE  <dgruber at mpe.mpg.de>

David Gruber (MPE) reports on behalf of the Fermi GBM Team: 

"At 11:09:29.94 UT on 31 July 2011, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 110731A (trigger 333803371 / 110731465)
which which was also detected by Fermi LAT (Bregeon et al. 2011, GCN 12218)
and Swift (Oates et al. 2011, GCN 12215).

The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 6 degrees.
Moreover, this burst was bright enough to result in a Fermi spacecraft 
autonomous rapid repoint (ARR) maneuver.

The GBM light curve consists of one pulse
with a duration (T90) of about 7.3 +/- 0.3 s (50-300 keV). 
The time-averaged spectrum from T0 s to T0+7.3 s is 
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.82 +/- 0.03 and
the cutoff energy, parameterized as Epeak, is 317 +/- 10 keV.

The event fluence (10-1000 keV) in this time interval is 
(2.218 +/- 0.006)E-05 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+0.128 s in the 10-1000 keV band 
is 20.9 +/- 0.5 ph/s/cm^2.

A Band function fits the spectrum equally well 
with Epeak= 304 +/- 13 keV, alpha = -0.80 +/- 0.03 and beta = -2.98 +/- 0.30. 


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