GCN Circular 18178

H.-F. Yu (MPE) and E. Burns (UAH)
report on behalf of the Fermi GBM Team:

"At 10:33:19.50 UT on 19 August 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150819B (trigger 461673203 / 150819440).

The on-ground calculated location, using the GBM trigger
data, is RA = 62.72, Dec = 40.60 (J2000 degrees,
equivalent to 04h 10m 53s, 40d 36'), 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 trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high peak flux of the GRB.
This ARR was accepted and the spacecraft slewed to the GBM in-flight
location. The initial angle from the Fermi LAT boresight
to the best location is 104 degrees .

The GBM light curve consists of two pulses
with a duration (T90) of about 0.96 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+0.896 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.04 +/- 0.02 and
the cutoff energy, parameterized as Epeak, is 532 +/- 27 keV

The event fluence (10-1000 keV) in this time interval is
(7.6 +/- 0.1)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.000 s in the 10-1000 keV band
is 148.4 +/- 3.8 ph/s/cm^2.

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