[vsnet-grb-info 19410] GRB 170522A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21126
SUBJECT: GRB 170522A: Fermi GBM detection
DATE:    17/05/23 00:30:48 GMT
FROM:    Matthew Stanbro at UAH/Fermi  <mcs0001 at uah.edu>

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

"At 15:45:35.28 UT on 22 May 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170522A (trigger 517160740 / 170522657).
The on-ground calculated location, using the GBM trigger
data, is RA = 135.45, DEC = 27.12, with an uncertainty
of 1.0 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 GBM ground location is 50 degrees.

The GBM light curve consists of 1 peak
with a duration (T90) of about 7 s (50-300 keV).
The time-averaged spectrum from T0-0.00 s to T0+8.32 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.41 +/- 0.02 and
the cutoff energy, parameterized as Epeak, is 344 +/- 8 keV.

The event fluence (10-1000 keV) in this time interval is
(2.31 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.58 s in the 10-1000 keV band
is 23.35 +/- 0.37 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 314 +/- 11 keV, alpha = -0.36 +/- 0.03 and beta = -2.63 +/-
0.15.


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