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GCN Circular 8549

Subject
GRB 081122: Fermi GBM detection
Date
2008-11-24T17:05:13Z (15 years ago)
From
Sheila McBreen at MPE <smcbreen@mpe.mpg.de>
Sheila McBreen (UCD/MPE) reports on behalf of the
Fermi GBM Team:

"At 12:28:12.21 UT on 22 November 2008, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 081122 (trigger 249049693 / 081122520).

The on-ground calculated location, using the GBM trigger
data, is RA = 338.7, DEC = +38.4 (J2000 degrees,
equivalent to 22 h 35 m, +38 d 24 '), with an uncertainty
of 1.2 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 21 degrees.
This event generated an Autonomous Repoint Recommendation from GBM,
which was accepted by the LAT and spacecraft. A 5 hour pointed mode
observation was initiated at the location of this burst.

The GBM light curve consists of 3 pulses
with a duration (T90) of about 26 s (8-1000 keV).
The time-averaged spectrum from T0-1 s to T0+26 s is
adequately  fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.77 +/-0.07 and
the cutoff energy, parameterized as Epeak, is 200.7 +/-15.7  keV
(chi squared  431.7 for 353 d.o.f.).

A Band function fits the spectrum equally well
(chi squared 431.3 for 352 d.o.f.) with Epeak = 158.6 +/- 17.6 keV,
alpha = -0.63 +/- 0.15 , and beta = -2.24 +/- 0.20.

The event fluence (8-1000 keV) in this time interval is
(9.6 +/- 1.1) E-6 erg/cm^2 (Band model). The 64 ms
peak photon flux  measured  starting from T0+0.756 s
in the 8-1000 keV band is 30.0 +/- 3.0 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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