TITLE:   GCN CIRCULAR
NUMBER:  42170
SUBJECT: GRB 251003A: Fermi GBM Observation
DATE:    25/10/08 18:10:09 GMT
FROM:    Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu>

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

"At 01:58:31.96 UT on 03 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251003A (trigger 781149516/251003082),
which was also detected by Swift BAT (A. P. Beardmore et al. 2025, GCN 42070).
The Fermi GBM on-ground location is consistent with the Swift BAT position.
GTC/OSIRIS+ detected a spectroscopic redshift z = 4.412 (R. Sanchez-Ramirez et al. 2025, GCN 42086).

The angle from the Fermi LAT boresight is 56 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 10 s (50-300 keV). The time-averaged spectrum
from T0-4.1 to T0+6.1 s is best fit by
a simple power law function with index -1.7 +/- 0.1.
A Comptonized function fits equally well with a Epeak of 118 +/- 35 and alpha of -1.3 +/- 0.2.

The event fluence (10-1000 keV) in this time interval is
(1.1 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-1.5 s in the 10-1000 keV band is 1.6 +/- 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/"