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GCN Circular 12390

GCN for GRB 110921B
2011-09-23T21:34:05Z (13 years ago)
Peter Jenke at MSFC <>
Peter Jenke (MSFC)/ Sylvain Guiriec (UAH)
report on behalf of the Fermi GBM Team:

"At 21:52:45.09 UT on 21 09 2011, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 110921B (trigger 338334767 / 110921.912).

The on-ground calculated location, using the GBM trigger
data, is RA = 17.95, DEC = -27.74 (J2000 degrees,
equivalent to 01 h 11.8 m, -27 d 44.4 m'), with an uncertainty
of 1.0 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 36.00 degrees.

The GBM light curve shows two main peaks with the
first being double peaked.  Moreover, this burst was
bright enough to result in a Fermi spacecraft 
autonomous rapid repoint (ARR) maneuver.
The burst had a duration (T90) of about 17 s (50-300 keV).
The time-averaged spectrum from T0+0.003 s to T0+23.552 s is
adequately fit by a Band function with Epeak = 513.0 +/- 31.3 keV,
alpha = -0.95 +/- 0.02, and beta = -2.23 +/- 0.10
(Chi squared 695.1 for 494 d.o.f.).

The event fluence (10-1000 keV) in this time interval is
(3.881 +/- 0.054)E-05 erg/cm^2. The peak photon flux measured
starting from T0+0.003 s in the 10-1000 keV band
is 7.558 +/- 0.068 ph/s/cm^2.

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