{
  "bibcode": "2025GCN.40004....1B",
  "submittedHow": "web",
  "circularId": 40004,
  "eventId": "GRB 250331D",
  "createdOn": 1743514425530,
  "format": "text/plain",
  "submitter": "Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi@ba.infn.it>",
  "body": "E. Bissaldi (Politecnico and INFN Bari), C. Meegan  (UAH)\nand A. Holzmann Airasca (Univ. Trento and INFN Bari)\nreport on behalf of the Fermi GBM Team:\n\n\n\"At 05:49:17.01 UT on 31 March 2025, the Fermi Gamma-Ray Burst Monitor (GBM)\ntriggered and located GRB 250331D (trigger 765092962 / 250331243),\nwhich was also detected by the Swift/BAT-GUANO (Ronchini et al. 2025, GCN 39979).\nThe GBM on-ground location is consistent with the Swift position.\n\nThe angle from the Fermi LAT boresight at the GBM trigger time is 27 degrees.\n\nThe GBM light curve consists of a single emission episode\nwith a duration (T90) of about 9 s (50-300 keV).\nThe time-averaged spectrum from T0-2.5 s to T0+6.4 s is\nadequately fit by a power law function with an exponential\nhigh-energy cutoff. The power law index is -1.12 +/- 0.27 and\nthe cutoff energy, parameterized as Epeak, is 91 +/- 20 keV.\n\nThe event fluence (10-1000 keV) in this time interval is\n(6.1 +/- 0.8)E-07 erg/cm^2. The 1-sec peak photon flux measured\nstarting from T0-0.64 s in the 10-1000 keV band\nis 2.2 +/- 0.2 ph/s/cm^2.\n\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/\"",
  "subject": "GRB 250331D: Fermi GBM observation"
}