TITLE: GCN CIRCULAR NUMBER: 42783 SUBJECT: GRB 251118A: Fermi GBM Observation DATE: 25/11/20 19:37:15 GMT FROM: Eva MP <eva.palafox@gmail.com> Eva Palafox (INAOE) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 20:31:30.09 UT on 18 November 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251118A (trigger 785190695/251118855), which was also detected by Fermi-LAT (R. Gupta et al. 2025, GCN 42752), Swift/XRT (J.P. Osborne et al. 2025, GCN 42782), GECAM-B (Yang-Zhao Ren et al., 2025, GCN 42779) and NuSTAR (G. Waratkar et al. 2025, GCN 42774). The Fermi GBM final real-time localization (GCN 42743) is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 69 degrees. The GBM light curve consists of a faint emission episode, followed by very bright emission episodes, with a total duration (T90) of about 46.6 s (50-300 keV). The time-averaged spectrum from T0-2.8 to T0+87.3 s is best fit by a Comptonized function with Epeak = 149.3 +/- 2.0 keV, and alpha = -1.40 +/- 0.01. A Band function fits equally well with Epeak = 134.0 +/- 2.7, alpha = -1.36 +/- 0.01, and beta = -2.56 +/- 0.06. The event fluence (10-1000 keV) in this time interval is (1.03 +/- 0.01)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+52 s in the 10-1000 keV band is 96 +/- 0.7 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/42783. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...