TITLE: GCN CIRCULAR NUMBER: 38806 SUBJECT: GRB 250103A: Fermi GBM Observation DATE: 25/01/03 21:19:29 GMT FROM: atrigg2@lsu.edu

A. C. Trigg (LSU), U. Pathak (IITB) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 09:57:46.56 UT on 03 January 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250103A (trigger 757591071/250103415). which was also detected by SVOM (Y. Wang et al. 2025, GCN 38787). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position.

The angle from the Fermi LAT boresight is 28 degrees.

The GBM light curve an initial emission followed by two smaller peaks with a duration (T90) of about 118 s (50-300 keV). The time-averaged spectrum from T0-7.6 to T0+112.3 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.75 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 33 +/- 5 keV.

The event fluence (10-1000 keV) in this time interval is (5.5 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+4.3 s in the 10-1000 keV band is 2.8 +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak= 32 +/- 4 keV, alpha = -1.70+/- 0.13 and beta = -2.65 +/- 0.38.

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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