[vsnet-grb-info 8411] GRB 090922A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9929
SUBJECT: GRB 090922A: Fermi GBM detection
DATE:    09/09/23 07:26:52 GMT
FROM:    Arne Rau at MPE  <arau at mpe.mpg.de>

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

"At 12:56:42.14  UT on 22 September 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090922A (trigger 275317004  / 090922539).

The on-ground calculated location, using the GBM trigger
data, is RA = 17.1, DEC = 74.3 (J2000 degrees,
equivalent to 17h 06m, 74d 18'), with an uncertainty
of 1 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 19 degrees.
Moreover, this burst was bright enough to result in
a Fermi spacecraft re-pointing maneuver.

The GBM light curve shows a bright peak of approximately 10s duration
followed by a weaker pulse approx. 60s later. The burst duration (T90) 
is 92 +/ 3 s (8-1000 keV).
The time-averaged spectrum of the main peak from T+0.003 s to T0+10.240 
s is
best fit by a Band function with Epeak = 139.3 +/- 6.6 keV,
alpha = -0.77 +/- 0.05, and beta = -2.28 +/- 0.07 (chi squared 1217/921 
d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(1.14 +/- 0.02)E-05 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+2.048 s in the 8-1000 keV band
is 15.6 +/- 0.04 ph/s/cm^2.

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