TITLE:   GCN CIRCULAR
NUMBER:  34501
SUBJECT: GRB 230818A: Fermi GBM Observation
DATE:    23/08/20 18:27:14 GMT
FROM:    Cori Fletcher at USRA <cfletcher@usra.edu>

P. Veres (UAH), C. Fletcher (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 23:27:35.37 UT on 18 August 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230818A (trigger 714094060/230818977).
which was also detected by Swift-BAT (A. Tohuvavohu et al. 2023, GCN 34479) and AstroSat (B. Pari et al. 2023, GCN 34492).
The Fermi GBM Final Real-time Localization (GCN 34478) is consistent with the Swift-BAT position.

The angle from the Fermi LAT boresight is 79 degrees.

The GBM light curve consists of a couple peaks with a duration (T90)
of about 10 s (50-300 keV). The time-averaged spectrum
from T0-1.5 to T0+13.8 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.02 +/- 0.06 and the cutoff energy,
parameterized as Epeak, is 260 +/- 30 keV.

The event fluence (10-1000 keV) in this time interval is
(5.6 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.58 s in the 10-1000 keV band is 10.2 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"