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GCN Circular 8664

Subject
GRB 081209: Fermi GBM detection
Date
2008-12-12T21:24:02Z (15 years ago)
From
Colleen A. Wilson at NASA/MSFC/NSSTC <colleen.wilson@nasa.gov>
Colleen A. Wilson-Hodge (NASA/MSFC) and Valerie Connaughton (UAH)
report on behalf of the Fermi GBM Team:

"At 23:41:56.39 UT on 9 December 2008, the Fermi Gamma-Ray Burst Monitor
(GBM) triggered and located GRB 081209 (trigger 250558317 / 081209981).

The on-ground calculated location, using the GBM trigger data, is
RA = 45.3, DEC = 63.5 (J2000 degrees, equivalent to 02 h 20 m, 68 d 52'),
with an uncertainty of 4.9 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic error which is
currently estimated to be 2 to 3 degrees). This location overlaps the IPN
arc reported in Golenetskii et al. 2008 (GCN Circular #8646).
 
The angle from the Fermi LAT boresight is 109 degrees.

The GBM light curve consists of a single peak with a duration (T90) of
about 0.4 s (8-1000 keV). The time-averaged spectrum from T0-0.110 s to
T0+0.210 s is best fit by a Band function with Epeak = 808 +/- 163 keV,
alpha = -0.5 +/- 0.1, and beta = -2.0 +/- 0.1. (chi squared 321.85 for
360 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(5.9 +/- 0.3)E-07 erg/cm^2. The 1-sec photon flux measured starting from
T0-0.110 s in the 8-1000 keV band is 7.8 +/- 0.4 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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