TITLE:   GCN CIRCULAR
NUMBER:  23118
SUBJECT: GRB 180809A: Fermi GBM observation
DATE:    18/08/10 13:00:48 GMT
FROM:    Elisabetta Bissaldi at INFN,Bari  <elisabetta.bissaldi@ba.infn.it>

E. Bissaldi (Politecnico & INFN Bari)
reports on behalf of the Fermi GBM Team:


"At 11:38:12.08 UT on 9 August 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180809A (trigger 555507497 / 180809485),
which was also detected by MAXI/GSC (Yatabe et al. 2018, GCN 23103) and
Swift/XRT (D'Elia et al. 2018, GCN 23106).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 60 degrees.

The GBM light curve consists of multiple emission episodes
with a duration (T90) of about 220 s (50-300 keV).
The time-averaged spectrum of the main emission episode
from T0-5 s to T0+15 s is adequately fit by a power law
function with an exponential high-energy cutoff.
The power law index is -1.37 +/- 0.06 and the cutoff energy,
parameterized as Epeak, is 620 +/- 230 keV.

The event fluence (10-1000 keV) in this time interval is
(6.8 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.2 s in the 10-1000 keV band is 4.0 +/- 0.3 ph/s/cm^2.


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