[vsnet-grb-info 19762] GRB 170830A: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21776
SUBJECT: GRB 170830A: Fermi GBM observation
DATE:    17/08/31 17:04:28 GMT
FROM:    Elisabetta Bissaldi at U.Innsbruk/IAPP  <Elisabetta.Bissaldi at uibk.ac.at>

M. Stanbro (UAH), E. Bissaldi (Politecnico & INFN Bari)
and C. Meegan (UAH) report on behalf of the Fermi GBM Team:


"At 03:14:01.95 UT on 30 August 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170830A (trigger 525755646 / 170830135).
This trigger is likely associated with the transient source
reported by MAXI/GSC (Yoneyama et al., GCN 21761), which was also detected
by AstroSat (Bhalerao et al., GCN 21773).

The on-ground calculated location, using the GBM trigger
data, is

RA = 275.9, DEC = -4.0,

with an uncertainty of 2.6 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 100 degrees.

The GBM light curve shows two peaks
with a duration (T90) of about 110 s (50-300 keV).
The time-averaged spectrum from T0 to T0+92 s is
adequately fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.54 +/- 0.07 and
the cutoff energy, parameterized as Epeak, is 180 +/- 40 keV.

The event fluence (10-1000 keV) in this time interval is
(4.20 +/- 0.11)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0 in the 10-1000 keV band
is 4.6 +/- 0.4 ph/s/cm^2.


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