TITLE:   GCN CIRCULAR
NUMBER:  23153
SUBJECT: GRB 180818B: Fermi GBM observations
DATE:    18/08/18 23:14:07 GMT
FROM:    Peter Veres at UAH  <veresp@gmail.com>

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

"At 12:28:57.24 UT on 18 August 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180818B (trigger 556288142 / 180818520).
which was also detected by the Swift/BAT
(Marshall et al., GCN 23149). The GBM on-ground location is consistent
with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 89 degrees.

The GBM light curve consists of two separate emission episodes
with a duration (T90) of about 169 s (50-300 keV).
The time-averaged spectrum from T0-16 s to T0+125 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is 1.8 +/- 1.32 and
the cutoff energy, parameterized as Epeak, is 78 +/- 9 keV.

The event fluence (10-1000 keV) in this time interval is
(4.7 +/- 0.7)E-7 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-2.4 s in the 10-1000 keV band
is 2.1 +/- 0.2 ph/s/cm^2.

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