[vsnet-grb-info 19721] GRB 170817B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21540
SUBJECT: GRB 170817B: Fermi GBM detection
DATE:    17/08/18 04:12:29 GMT
FROM:    Oliver J Roberts at USRA/NASA  <oliver.roberts at nasa.gov>

O.J. Roberts (USRA) and C. Meegan (UAH) report on behalf of 
the Fermi GBM Team:

"At 21:47:34.43 UT on 17 August 2017, the Fermi Gamma-Ray 
Burst Monitor triggered and located GRB 170817B 
(trigger 524699259 / 170817908). The on-ground calculated 
location, using the GBM trigger data, is RA = 83.0, 
DEC = +50.1, with an uncertainty of 3.7 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 initial angle from the Fermi LAT boresight to
the GBM best location is 90 degrees.

The GBM triggered multiple short unresolvable pulses over a
total duration (T90) of 2.6 s (50-300 keV).
The time-averaged spectrum from T0+0.0 to T0+2.6 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.87 +/- 0.06 and
the cutoff energy, parameterized as Epeak, is 1120 +/- 228 keV

The event fluence (10-1000 keV) in this time interval is
(4.93 +/- 0.16)E-06 erg/cm^2. The 64 ms peak photon flux measured
starting from T0+0.0 s in the 10-1000 keV band
is 10.4 +/- 1.6 ph/s/cm^2.


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