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GCN Circular 8678

Subject
GRB 081215A: Fermi GBM detection
Date
2008-12-17T22:42:55Z (15 years ago)
From
Rob Preece at UAH <Rob.Preece@nasa.gov>
Robert Preece (UAH) reports on behalf of the Fermi GBM Team:

"At 18:48:36.85 UT on 15 December 2008, the Fermi Gamma-Ray Burst  
Monitor
triggered and located GRB 081215 (trigger 251059717 / 081215784).

The on-ground calculated location, using the GBM trigger
data, is RA = 135.0, DEC = +53.8 (J2000 degrees,
equivalent to 09 h 00 m 00.00, 53 d 48 '), with an uncertainty
of 1.0 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 86 degrees.

The on-board GBM Flight Software localization for this very bright
burst, as reported in the GCN Notices, was consistent
with a position on the Earth's surface, likely due to a large scattered
flux from the Earth. This resulted in an autonomous and erroneous
"100%  Below horizon" classification for this event which prevented an
automated ground localization from being sent through the GCN notice
system.

The GBM light curve consists of a very hard narrow pulse on
top of a broader emission episode,
with a duration (T90) of about 7.7 s (8-1000 keV).
The time-averaged spectrum from T0-1.79 s to T0+13.57 s is
best fit by a Band function with Epeak = 304 +/- 11 keV,
alpha = -0.585 +/- 0.022, and beta = -2.066 +/- 0.038.

The event fluence (8-1000 keV) in this time interval is
(3.54 +/- 0.05)E-6 erg/cm^2. The 1-sec photon flux measured
starting from T0+1.28 s in the 8-1000 keV band
is 68.9 +/- 1.0 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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