GCN Circular 41662

S. Bala (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 01:30:00.49 UT on 02 September 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250902A (trigger 778469405/250902062).
The Fermi-GBM position was reported in GCN 41648
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  (Fermi GBM Team 2025).

The angle from the Fermi LAT boresight is 78 degrees.

The GBM light curve consists of a bright pulse with a duration (T90)
of about 8.4 s (50-300 keV). The time-averaged spectrum
from T0-1.0 to T0+17.4 s is best fit by Band function with
a Band function with Epeak = 257 +/- 13 keV,
alpha = -1.25 +/- 0.02, and beta = -2.31 +/- 0.1.

A power law function with an exponential high-energy cutoff fits
the spectrum equally well with a with power law index = -1.28 +/- 0.01
and Epeak = 294 +/- 10 keV.

The event fluence (10-1000 keV) in this time interval is
(3.06 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.5 s in the 10-1000 keV band is 43.5 +/- 0.5 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/"