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GCN Circular 21520

Subject
GRB 170817A: Fermi GBM detection
Date
2017-08-17T20:00:07Z (7 years ago)
From
Andreas von Kienlin at MPE <azk@mpe.mpg.de>
A. von Kienlin (MPE), C. Meegan (UAH) and A. Goldstein (USRA)
report on behalf of the Fermi GBM Team:

"At 12:41:06.47 UT on 17 August 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170817A (trigger 524666471 / 170817529).

The on-ground calculated location, using the GBM trigger
data, is RA = 176.8, DEC = -39.8 (J2000 degrees,
equivalent to 12 h 47 m, -39 d 48'), with an uncertainty
of 11.6 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).

The angle from the Fermi LAT boresight at the GBM trigger time is 91 degrees.

The GRB light curve shows a weak short pulse
with a duration (T90) of about 2 s (50-300 keV).
The time-averaged spectrum from T0-0.512 s to 2.048 s is
well fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.89 +/- 0.5 and
the cutoff energy, parameterized as Epeak, is 82 +/- 21 keV

The event fluence (10-1000 keV) in this time interval is
(2.3 +/- 0.4)E-07 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0-0.32 s in the 8-1000 keV band
is 1.9 +/- 0.2 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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