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GCN Circular 8822

Subject
GRB 090117C - Fermi GRB Detection
Date
2009-01-18T06:15:23Z (15 years ago)
From
Valerie Connaughton at MSFC <valerie@nasa.gov>
Valerie Connaughton (UAH) reports on behalf of the Fermi GBM Team:

"At 15:10:40.18 UT on 17 Jan 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090117C (trigger 253897842 / 090117632).

The on-ground calculated location, using the GBM trigger
data, is RA = 117.6, DEC = -40.3 (J2000 degrees,
equivalent to 07h 50m, -40d 18'), with an uncertainty
of 1.8 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 54 degrees.

The GBM light curve consists of a precursor lasting tens
of seconds until trigger time, followed by a single episode with
substructure lasting a further 35 s.  The total duration (T90)
between 8 and 1000 keV is about 86 s.
 
The time-averaged spectrum of the main emission
from T0-2 s to T0+29 s is best fit by a Band function with
Epeak = 247 +/- 41 keV, alpha = -1.0 +/- 0.1, and
beta = -2.1 +/- 0.2, giving an 8-1000 keV fluence of
(1.1 +/- 0.1) E-5 erg/cm^2.  

The precursor spectrum from T0-55 sec to T0-6 s is best fit
using a power law function with an exponential
high energy cutoff.  The power law index is -1.3 +/- 0.1 and
the cutoff energy, parameterized as Epeak, is 147 +/- 38 keV.
The 8-1000 keV fluence of the precursor is
(3.9 +/- 0.5) E-6 erg/cm^2.

A 1-sec peak photon flux of 4.2 +/- 0.7 ph/s/cm^2
in the 8-1000 keV band is measured starting at T0+22.5 s.

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