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GCN Circular 10266

Subject
GRB 091208B: Fermi GBM observation
Date
2009-12-08T17:42:47Z (14 years ago)
From
Sheila McBreen at MPE <smcbreen@mpe.mpg.de>
S. McBreen (UCD/MPE) reports on behalf of
the Fermi GBM Team:

"At 09:49:57.96 UT on 08 December 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 091208B (trigger 281958599 / 091208410)
which was also detected by the Swift-BAT (Pagani et al. 2009, GCN 10256).
The GBM on-ground location is consistent with the Swift position.
This burst was also independently detected by INTEGRAL SPI-ACS.

The angle from the Fermi LAT boresight is 56 degrees.
Moreover, this burst was bright enough to result in
a Fermi spacecraft repointing maneuver.

The GBM light curve consists of two pulses
with a duration (T90) of about 15 s (8-1000 keV).
The time-averaged spectrum from T0-0.128 s to T0+14.592 s is
well fit by a power law function with an exponential
high energy cutoff.  The power law index is -1.48 (+0.05/-0.05) and
the cutoff energy, parameterized as Epeak, is 144.20 (+18.00/-13.90) keV
(CSTAT 829 for 604 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(5.8 +/- 0.2)E-06 erg/cm^2. The 0.128 sec peak photon flux measured
starting from T0+8.45 s in the 8-1000 keV band is 32.4 +/- 1.1 ph/s/cm^2.

A Band function fits the spectrum equally well (CSTAT 827 for 603 d.o.f.)
with Epeak= 124.00 (+20.10/-19.40) keV, alpha = -1.44 (+0.07/-0.06)
and beta = -2.32 (+0.19/-0.47).

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