GCN Circular 21717

S. Poolakkil (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 19:38:56.48 UT on 26 August 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170826B (trigger 525469141/ 170826819).

The on-ground calculated location, using the GBM trigger
data, is RA = 327.7, DEC = -31.8, with an uncertainty
of 1 degree (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 fluence
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 GBM ground best location is 110 degrees.

The GBM light curve shows multiple overlapping pulses
with a duration (T90) of about 11 s (50-300 keV).
The time-averaged spectrum from T0-2.0 to T0+20.5 s is
best fit by a Band function with Epeak = 385 +/- 24 keV,
alpha = -0.98 +/- 0.02, and beta = -2.24 +/- 0.10.

The event fluence (10-1000 keV) in this time interval is
(3.592 +/- 0.052)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.0 s in the 10-1000 keV band
is 25.4 +/- 0.5 ph/s/cm^2.

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

-- 
Suraj Poolakkil
Fermi GBM Graduate Research Assistant
Dept. of Space Science
University of Alabama in Huntsville