TITLE: GCN CIRCULAR NUMBER: 42846 SUBJECT: GRB 251121A: Fermi GBM Observation DATE: 25/11/26 20:32:32 GMT FROM: Angus Jameson <abj0023@uah.edu> S. Bala (USRA), A. Jameson (UAH), and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 16:30:58.99 UT on 21 November 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251121A (trigger 785435463/251121688), which was also detected by Swift/BAT-GUANO (DeLaunay et al. 2025 GCN 42795). The Fermi GBM on-ground location (GCN 42790) is consistent with the Swift/BAT-GUANO position. The angle from the Fermi LAT boresight is 100 degrees. The GBM light curve single peak with a duration (T90) of about 0.3 s (50-300 keV). The time-averaged spectrum from T0-0.2 to T0+0.3 s is best fit by a simple power law function with index -1.31 +/- 0.07. The event fluence (10-1000 keV) in this time interval is (2.8 +/- 0.3)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0-0.064 s in the 10-1000 keV band is 5 +/- 1 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/42846. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...