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GCN Circular 14094

Subject
GRB 121217A: Fermi GBM observation
Date
2012-12-18T10:26:28Z (11 years ago)
From
David Gruber at MPE <dgruber@mpe.mpg.de>
David Yu and David Gruber (both MPE)
report on behalf of the Fermi GBM Team:

"At 07:30:01.58 UT on 17 December 2012, the Fermi Gamma-Ray Burst Monitor
triggered and located a burst (trigger 377422204 / 121217313), whose
location is consistent with the Swift GRB 121217A (Siegel et al. GCN 14089)
which triggered BAT ~13 minutes prior to the GBM.
Upon closer examination, we found that GRB 121217A is also present in the 
GBM data. GBM did not trigger on this earlier emission period owing to the
triggering being disabled while Fermi was passing through a
region of high geomagnetic latitude.

The GBM light curve consists of two epochs of emission,
separated by an epoch of quiescence of about 700 s.
The duration of the first pulse is about 50 s while 
the second pulse is about 30 s long. The overall event T90 is 
about 780 s (50-300 keV).
The time-averaged spectrum of the first emission epoch,
from T0-749.6 s to T0-704.5 s, is well fit by a power law 
function with an exponential high-energy cutoff.  The power law index 
is -1.20 +/- 0.12 and the cutoff energy, parameterized as Epeak, 
is 264 +/- 75 keV. The time-averaged spectrum of the 
second emission epoch, from T0-8.2 s to T0+24.6 s, is well fit 
by the same model, having a power law index of -1.29 +/- 0.14 and an 
Epeak of 184 +/- 56 keV.

The event fluence (10-1000 keV) over the overall event is
(1.11 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2.68 s in the 10-1000 keV band
is 3.47 +/- 0.29 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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