TITLE:   GCN CIRCULAR
NUMBER:  21504
SUBJECT: GRB 170816A: Fermi GBM detection
DATE:    17/08/17 10:04:36 GMT
FROM:    Andreas von Kienlin at MPE  <azk@mpe.mpg.de>

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

"At 14:23:03.96 UT on 16 August 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170816A (trigger 524586188 / 170816599).
The on-ground calculated location, using the GBM trigger
data, is RA = 351.4, DEC = +19.1, with an uncertainty
of 2.2 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 97 degrees.

This burst was also independently detected by INTEGRAL SPI-ACS.

The GBM triggered on an initial bright peak that
was followed ~1 s later by a slightly dimmer peak. The
total duration (T90) was about 2 s (50-300 keV).
The time-averaged spectrum from T0-0.064 to T0+1.600 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.5 +/- 0.1  and
the cutoff energy, parameterized as Epeak, is 1250.00 +/- 150.00 keV

The event fluence (10-1000 keV) in this time interval is
(4.0+/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.45 s in the 10-1000 keV band
is 7.3 +/- 0.3 ph/s/cm^2.

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