TITLE:   GCN CIRCULAR
NUMBER:  42410
SUBJECT: GRB 251022A: Fermi GBM Observation
DATE:    25/10/23 22:45:23 GMT
FROM:    oindabimukherjee@gmail.com

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

"At 22:34:15.26 UT on 22 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251022A (trigger 782865260/251022940)
which was also detected by Fermi-LAT ( N. Di Lalla et al. 2025, GCN 42384), 
MASTER OT (V. Lipunov et al. 2025, GCN 42395),
and Swift/BAT-GUANO (James DeLaunay et al. 2025, GCN 42409).
The Fermi GBM on-ground location is consistent with the Fermi-LAT position.

The angle from the Fermi LAT boresight is 36.5 degrees.

The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 99.6 s (50-300 keV). The time-averaged spectrum
from T0-1 to T0+107.5 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.88 +/- 0.04 and the cutoff energy,
parameterized as Epeak, is 154 +/- 5 keV.

The event fluence (10-1000 keV) in this time interval is
(2.16 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+100 s in the 10-1000 keV band is 12.4 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 138 +/- 7 keV, alpha = -0.8 +/- 0.05 and beta = -2.6 +/- 0.2.

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/"