TITLE:   GCN CIRCULAR
NUMBER:  34618
SUBJECT: GRB 230903A: Fermi GBM detection
DATE:    23/09/04 16:40:58 GMT
FROM:    Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>

O.J. Roberts (USRA), B. Mailyan (Florida Tech) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 17:22:58.81 UT on the 3rd September 2023 , the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 230903A (trigger 715454583 / 230903724) which was also detected 
by the Swift/BAT (A. D'ai et al. 2023, GCN 34610). The Fermi GBM Final Real-time Localization 
(GCN 34608) is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 98 degrees.

The GBM light curve consists of one pulse
with a duration (T90) of about 3 s (50-300 keV).
The time-averaged spectrum from T0-4.0 s to T0+1.0 s is
best fit by a simple power law function with index -1.78 +/- 0.09.

A power law function with an exponential high-energy cutoff fits
the spectrum equally well. The power law index is -1.27 +/- 0.33 
and the cutoff energy, parameterized as Epeak, is 95 +/- 31 keV.

The event fluence (10-1000 keV) in this time interval is
(5.87 +/- 0.85)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-1s in the 10-1000 keV band
is 2.0 +/- 0.2 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/"