{
  "submitter": "A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca@unitn.it>",
  "subject": "GRB 251221A: Fermi GBM Observation",
  "submittedHow": "web",
  "body": "A. Holzmann Airasca (UniTrento and INFN Bari) and S. Bala (USRA) report on behalf of\n the Fermi Gamma-ray Burst Monitor Team:\n \n \"At 05:24:28.61 UT on 21 December 2025, the Fermi Gamma-ray Burst Monitor (GBM)\n triggered and located GRB 251221A (trigger 787987473/251221225).\n which was also detected by Swift (Ambrosi et al. 2025, GCN 43166).\n The Fermi GBM on-ground location is consistent with the Swift position.\n \n The angle from the Fermi LAT boresight is 96 degrees.\n \n The GBM light curve consists of a single peak with a duration (T90)\n of about 28 s (50-300 keV). The time-averaged spectrum\n from T0-13.3 to T0+23.6 s is best fit by\n a power law function with an exponential high-energy cutoff.\n The power law index is -1.1 +/- 0.1 and the cutoff energy,\n parameterized as Epeak, is 330 +/- 100 keV.\n \n The event fluence (10-1000 keV) in this time interval is\n (4.2 +/- 0.5)E-06 erg/cm^2. The 1-sec peak photon flux measured\n starting from T0+1.4 s in the 10-1000 keV band is 2.0 +/- 0.2 ph/s/cm^2.\n \n A Band function fits the spectrum equally well\n with Epeak= 240 +/- 130 keV, alpha = -1.0 +/- 0.2 and beta = -1.8 +/- 0.2.\n \n The spectral analysis results presented above are preliminary;\n final results will be published in the GBM GRB Catalog:\n https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html\n \n For Fermi GBM data and info, please visit the official Fermi GBM Support Page:\n https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/\"",
  "circularId": 43174,
  "createdOn": 1766347983311,
  "eventId": "GRB 251221A",
  "format": "text/plain",
  "bibcode": "2025GCN.43174....1H"
}