[vsnet-grb-info 18397] GRB 160822672: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19845
SUBJECT: GRB 160822672: Fermi GBM detection
DATE:    16/08/23 01:10:37 GMT
FROM:    Rachel Hamburg at UAH  <rkh0007 at uah.edu>

R. Hamburg (UAH), C. Meegan (UAH), and A. Goldstein (USRA)
report on behalf of the Fermi GBM Team:

"At 16:07:40.01 UT on 22 August 2016, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 160822A (trigger 493574864 / 160822672).

The on-ground calculated location, using the GBM trigger
data, is RA = 270, DEC = +8, with an uncertainty
of 5 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 angle from the Fermi LAT boresight at the GBM trigger time is 58
degrees.

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 on-board
localization, 160 degrees from the LAT boresight.  The more reliable
on-ground
localization placed the GRB at a location ~100 deg away from the onboard
localization.  The ARR was then canceled and replaced with a short TOO
at the on-ground localization.

The GBM light curve shows a single peak
with a duration (T90) of about 0.4 s (50-300 keV).
The time-averaged spectrum from T0-0.13 s to T0+0.13 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.05 +/- 0.10 and
the cutoff energy, parameterized as Epeak, is 1166.00 +/- 560.00 keV.

The event fluence (10-1000 keV) in this time interval is
(7.33 +/- 0.49)E-07 erg/cm^2. The 0.064-sec peak photon flux measured
starting from T0+0.0 s in the 10-1000 keV band
is 22 +/- 2 ph/s/cm^2.

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