{
  "body": "A. von Kienlin (MPE) and C. Meegan (UAH) report on behalf of\nthe Fermi Gamma-ray Burst Monitor Team:\n\n\"At 10:17:17.29 UT on 08 December 2025, the Fermi Gamma-ray Burst Monitor (GBM)\ntriggered and located GRB 251208B (trigger 786881842/251208429).\nwhich was also detected by Fermi-LAT (E. Bissaldi et al. 2025, GCN 43034)\nand Swift/BAT-GUANO (GCN #43033). The Fermi GBM on-ground location was reported\nby the Fermi-GBM team in GCN 43028 and is consistent with the Fermi-LAT\nand Swift/BAT positions.\n\nThe GBM light curve shows a structured emission episode with a duration (T90)\nof about 62.5 s (50-300 keV). The time-averaged spectrum\nfrom T0-4.1 to T0+61.4 s is best fit by\na power law function with an exponential high-energy cutoff.\nThe power law index is -0.67 +/- 0.08 and the cutoff energy,\nparameterized as Epeak, is 250 +/- 20 keV.\n\nThe event fluence (10-1000 keV) in this time interval is\n(9.5 +/- 0.5)E-06 erg/cm^2. The 1-sec peak photon flux measured\nstarting from T0+55 s in the 10-1000 keV band is 2 +/- 0.2 ph/s/cm^2.\n\nThe spectral analysis results presented above are preliminary;\nfinal results will be published in the GBM GRB Catalog:\nhttps://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html\n\nFor Fermi GBM data and info, please visit the official Fermi GBM Support Page:\nhttps://fermi.gsfc.nasa.gov/ssc/data/access/gbm/\"",
  "submitter": "Andreas von Kienlin at MPE <azk@mpe.mpg.de>",
  "bibcode": "2025GCN.43046....1V",
  "circularId": 43046,
  "submittedHow": "email",
  "createdOn": 1765281118468,
  "eventId": "GRB 251208B",
  "subject": "GRB 251208B: Fermi GBM Observation"
}