TITLE: GCN CIRCULAR NUMBER: 42093 SUBJECT: GRB 251002A: Fermi GBM Observation DATE: 25/10/03 14:21:41 GMT FROM: Jacob Smith at Fermi-GBM Team jrs0118@uah.edu

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

"At 20:14:51.01 UT on 02 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251002A (trigger 781128896/251002844). which was also detected by SVOM/ECLAIRs (A. Saccardi et al. 2025, GCN 42060). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. VLT/X-shooter detected a spectroscopic redshift of z = 2.178 (A. Saccardi et al. 2025, GCN 42076).

The angle from the Fermi LAT boresight is 53 degrees.

The GBM light curve multiple emission episodes with a duration (T90) of about 26 s (50-300 keV). The time-averaged spectrum from T0-6.9 to T0+14.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.88 +/- 0.07 and the cutoff energy, parameterized as Epeak, is 180 +/- 10 keV.

The event fluence (10-1000 keV) in this time interval is (4.6 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+7.9 s in the 10-1000 keV band is 7.1 +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak= 140 +/- 20 keV, alpha = -0.7 +/- 0.1 and beta = -2.2 +/- 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/"

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