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/"
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