[vsnet-grb-info 8307] GRB 090820B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9832
SUBJECT: GRB 090820B: Fermi GBM detection
DATE:    09/08/21 07:48:55 GMT
FROM:    Arne Rau at MPE  <arau at mpe.mpg.de>

Arne Rau (MPE) reports on behalf of the Fermi GBM Team:

"At 12:13:16.70 UT on 20 August 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090820B (trigger 272463198 / 090820509).

The on-ground calculated location, using the GBM trigger
data, is RA = 318.3, DEC = -18.6 (J2000 degrees,
equivalent to 21 h 13 m, -18 d 36 '), with an uncertainty
of 9.6 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which is currently estimated to be 2 to 3 degrees).
 
The angle from the Fermi LAT boresight is 32 degrees.

The GBM light curve consists of two narrow peaks
with a duration (T90) of about 11.2 s (8-1000 keV).
The time-averaged spectrum from T0-0.128 s to T0+12.160 s is
best fit by a power law function with an exponential
high energy cutoff.  The power law index is -1.44 +/- 0.18 and
the cutoff energy, parameterized as Epeak, is 38.8 +/- 4.4 keV
(chi squared 336 for 356 d.o.f.)

The event fluence (8-1000 keV) in this time interval is
(1.16 +/- 0.07)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0-0.128 s in the 8-1000 keV band
is 6.1 +/- 0.4 ph/s/cm^2.

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