[vsnet-grb-info 19166] GRB170305A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20818
SUBJECT: GRB170305A: Fermi GBM detection
DATE:    17/03/05 20:28:27 GMT
FROM:    Matthew Stanbro at UAH/Fermi  <mcs0001 at uah.edu>

M. Stanbro (UAH), A. von Kienlin (MPE), and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 06:09:06.78 UT on 05 March 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170305A (trigger 510386951 / 17035256).

The on-ground calculated location, using the GBM trigger
data, is RA = 38.66, DEC = 12.09, with an uncertainty
of 3.7 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] ).

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 consists of 1 episode
with a duration (T90) of about 0.44 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+0.384 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.53 +/- 0.08 and
the cutoff energy, parameterized as Epeak, is 293 +/- 24 keV

The event fluence (10-1000 keV) in this time interval is
(1.29 +/- 0.07)E-06 erg/cm^2. The 64-msec peak photon flux measured
starting from T0+0.0 s in the 10-1000 keV band
is 31.0 +/- 1.6 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 233 +/- 35 keV, alpha = -0.42 +/- 0.13 and beta = -2.06 +/-
0.13.


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