TITLE:   GCN CIRCULAR
NUMBER:  42553
SUBJECT: GRB 251103A: Fermi GBM Observation
DATE:    25/11/03 16:33:54 GMT
FROM:    Rushikesh Sonawane at IISER, TVM <rushikesh23@iisertvm.ac.in>

R. Sonawane (IISER, TVM) and M. Godwin (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 04:46:28.11 UT on 03 November 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251103A (trigger 783837993/251103199),
which was also detected by SVOM/ECLAIRs (Hu et al. 2025, GCN 42534).
The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position.
NOT measured a spectroscopic redshift z = 0.76 (Izzo et al. 2025, GCN 42540).

The angle from the Fermi LAT boresight is 113 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 4 s (50-300 keV). The time-averaged spectrum
from T0-3.0 to T0+6.2 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.42 +/- 0.03 and the cutoff energy,
parameterized as Epeak, is 151 +/- 3 keV.

The event fluence (10-1000 keV) in this time interval is
(5.6 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.13 s in the 10-1000 keV band is 18.8 +/- 0.5 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 123 +/- 2 keV, alpha = -0.18 +/- 0.01 and beta = -2.4 +/- 0.1.

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/"