TITLE: GCN CIRCULAR NUMBER: 42965 SUBJECT: GRB 251201B: Fermi GBM Observation DATE: 25/12/02 20:57:29 GMT FROM: Eva Palafox at INAOE <eva.palafox@gmail.com> Eva Palafox (INAOE) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 16:26:24.22 UT on 01 December 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251201B (trigger 786299189/251201685), which was also detected by Swift BAT (M. J. Moss et al. 2025, GCN 42924), and Swift XRT (J.P. Osborne et al. 2025, GCN 42927). The Fermi GBM on-ground location (GCN 42923) is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 119 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 91 s (50-300 keV). The time-averaged spectrum from T0-22.5 to T0+105.5 s is best fit by a simple power law function with index -1.83 +/- 0.04. A power law function with an exponential high-energy cutoff fits equally well with power law index = -1.71 +/- 0.08 and Epeak = 269.8 +/- 166.0. The event fluence (10-1000 keV) in this time interval is (1.2 +/- 0.1)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+4.7 s in the 10-1000 keV band is 4 +/- 0.3 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/42965. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...