[vsnet-grb-info 19685] GRB 170808B: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21429
SUBJECT: GRB 170808B: Fermi GBM observation
DATE:    17/08/09 04:42:21 GMT
FROM:    Peter Veres at UAH  <veresp at gmail.com>

P Veres and C Meegan (both UAH)
report on behalf of the Fermi GBM Team:

"At 22:27:43.10 UT on 8 August 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170808B (trigger 523924068 / 170808936).

The on-ground calculated location, using the GBM trigger
data, is RA = 146.49, DEC = -2.96 (J2000 degrees,
equivalent to 09 h 46 m, -02 d 58 '), with an uncertainty
of 1 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] ).

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 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 69 degrees.

The GBM light curve shows multiple overlapping pulses
with a duration (T90) of about 17.7 s (50-300 keV).
The time-averaged spectrum from T0 to T0+27.1 s is
best fit by a Band function with Epeak = 262 +/- 5 keV,
alpha = -1.01+/- 0.01, and beta = -2.30 +/- 0.03.

The event fluence (10-1000 keV) in this time interval is
(1.176 +/- 0.005)E-4 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+15.9 s in the 10-1000 keV band
is 169.4 +/- 0.7 ph/s/cm^2.


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