[vsnet-grb-info 21085] GRB 180828A: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23183
SUBJECT: GRB 180828A: Fermi GBM observation
DATE:    18/08/29 04:19:38 GMT
FROM:    Oliver J Roberts at USRA/NASA  <oliver.roberts at nasa.gov>

O.J. Roberts (USRA/NASA) and C. Meegan (UAH) report on behalf
of the Fermi GBM Team:

"At 18:57:26.58 UT on 28 August 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180828A (trigger 557175451 / 180828790),
which was also detected by Swift (Beardmore et al. 2018, GCN 23182).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time using the
Swift-XRT position is 77 degrees.

The GBM light curve consists of multiple bright pulses with a duration
(T90) of 8.3 s (50-300 keV). The time-averaged spectrum from T0+1.5s to 
T0+11 s is best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.46 +/- 0.02 and the 
cutoff energy, parameterized as Epeak, is 358 +/- 9 keV.

A Band function fits the interval equally well, with 
Epeak =346 +/- 12 keV, alpha = -0.44 +/- 0.03 and
beta = -3.01 +/- 0.33.

The event fluence (10-1000 keV) over the T90 interval is
(3.39 +/- 0.5)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0 +8s in the 10-1000 keV band is 38 +/- 1 ph/s/cm^2.

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