[vsnet-grb-info 19165] GRB 170304A: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20813
SUBJECT: GRB 170304A: Fermi GBM observation
DATE:    17/03/04 12:01:08 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 00:04:26.07 UT on 04 March 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170304A (trigger 510278671 / 170304003).


The on-ground calculated location, using the GBM trigger
data, is RA = 330.50, DEC = -73.76 (J2000 degrees,
equivalent to 22 h 2 m, 73 d 46 '), with an uncertainty
of 6.7 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 69 degrees.

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 59 degrees.

The GBM light curve shows a single pulse
with a duration (T90) of about 0.16 s (50-300 keV).
The time-averaged spectrum from T0-0.1 s to T0+0.2 s is
adequately fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.02 +/- 0.23 and
the cutoff energy, parameterized as Epeak, is 76.4 +/- 9.8 keV.


The event fluence (10-1000 keV) in this time interval is
(2.1 +/- 0.2)E-7 erg/cm^2. The 64 ms peak photon flux measured
starting from T0 in the 10-1000 keV band is 24.1 +/- 1.5 ph/s/cm^2.

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