GCN Circular 23387

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


"At 14:09:42.53 UT on 28 October 2018,
the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 181028A
(trigger 562428587/ 181028590),
which was also detected by the
Fermi-LAT (Axelsson et al. 2018, GCN 23386
Not found
 
 
).
The GBM on-ground location is
consistent with the LAT position.

The angle from the Fermi-LAT boresight
at the GBM trigger time is 58 degrees.

The GBM light curve consists of multiple peaks
with a duration (T90) of about 30 s (50-300 keV).
The time-averaged spectrum from T0 to T0+30 s
is adequately by a power law function with
an exponential high-energy cutoff.
The power law index is -0.72 +/- 0.02 and
the cutoff energy, parameterized as Epeak,
is 326 +/- 10 keV.

The event fluence (10-1000 keV) in this time interval
is (3.35 +/- 0.05)E-05 erg/cm^2.
The 1-sec peak photon flux measured
starting from T0+26.5 s in the 10-1000 keV band
is 10.3 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 306 +/- 13  keV, alpha = -0.69 +/- 0.03,
and beta = -2.66 +/- 0.24.


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