GCN Circular 19443

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

"At 09:13:58.03 UT on 21 May 2016, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 160521B (trigger 485514842 / 160521385).

The on-ground calculated location, using the GBM trigger
data, is RA = 156, Dec = 76 (J2000 degrees, equivalent 
to 15h 25m, 76d 17'), 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] ).

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

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 GBM ground location is 47 degree.

The GBM light curve shows a single pulse with sub-structures
with a duration (T90) of about 2.8 s (50-300 keV).
The time-averaged spectrum from T0+0.002 s to T0+3.520 s is
best fit by a Band function with Epeak = 155 +/- 5 keV,
alpha = -0.45 +/- 0.03, and beta = -2.54 +/- 0.07.

The event fluence (10-1000 keV) in this time interval is
(1.25 +/- 0.02)E-05 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+0.960 s in the 10-1000 keV band
is 42.4 +/- 0.4 ph/s/cm^2.

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