TITLE:   GCN CIRCULAR
NUMBER:  11015
SUBJECT: GRB 100728B: Fermi GBM observation
DATE:    10/07/28 13:47:40 GMT
FROM:    Andreas von Kienlin at MPE  <azk@mpe.mpg.de>

A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: 

"At 10:31:54.97 UT on 28 July 2010, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 100728B (trigger 302005916 / 100728439),
which was also detected by the Swift-BAT (Morris et al. 2008, GCN 11009)
The GBM on-ground location is consistent with the Swift position.
 
The angle from the Fermi LAT boresight is 57.1 degrees.

The GBM light curve shows a single pulse
with a duration (T90) of about 11.8 +/- 2.4 s (50-300 keV). 
The time-averaged spectrum from T0-1.024 s to T0+5.632 s is 
well fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.9 +/- 0.1 and
the cutoff energy, parameterized as Epeak, is 131 +/- 15 keV
(chi squared 1043 for 599 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(2.4 +/- 0.1)E-06 erg/cm^2. The 1.024-sec peak photon flux measured 
starting from T0+1.22 s in the 8-1000 keV band 
is 6.2  +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 1037 
for 598 d.o.f.) with Epeak= 104 +/- 14 keV, alpha = -0.8 +/- 0.2 
and beta = -2.2 +/-0.2. 

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