TITLE: GCN CIRCULAR NUMBER: 42118 SUBJECT: GRB 251005C: Fermi GBM Observation DATE: 25/10/06 03:46:34 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu> Jacob Smith (UAH), B. Mailyan (Florida Tech) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 16:06:54.00 UT on 05 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251005C (trigger 781373219/251005671), which was also detected by Swift BAT (K. L. Page et al. 2025, GCN 42113). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 98 degrees. The GBM light curve consists of a double emission episode with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+5.248 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.9 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 2136 +/- 866 keV. The event fluence (10-1000 keV) in this time interval is (3.2 +/- 0.2)E-06 erg/cm^2. The 64-millisec peak photon flux measured starting from T0+0.58 s in the 10-1000 keV band is 6.1 +/- 1.2 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/" View this GCN Circular online at https://gcn.nasa.gov/circulars/42118. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...