{
  "circularId": 41411,
  "version": 3,
  "subject": "GRB 250818A: Fermi GBM Observation",
  "createdOn": 1755529308996,
  "eventId": "GRB 250818A",
  "editedOn": 1755529435340,
  "editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Cuán de Barra at UCD <cuan.debarra@ucdconnect.ie>",
  "submitter": "Cuán de Barra at UCD <cuan.debarra@ucdconnect.ie>",
  "submittedHow": "web",
  "body": "C. de Barra (University College Dublin) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:\n\n\"At 01:31:23.00 UT on 18 August 2025, the Fermi Gamma-ray Burst Monitor (GBM)\ntriggered and located GRB 250818A (trigger 777173487/250818063)\nwhich was also detected by Swift BAT (S. B. Cenko et al. 2025, GCN 41403).\nThe Fermi GBM on-ground location is consistent with the Swift BAT position.\n\nThe angle from the Fermi LAT boresight is 146 degrees.\n\nThe GBM light curve consists of multiple emission episodes with a duration (T90)\nof about 101 s (50-300 keV). The time-averaged spectrum\nfrom T0-9.2 to T0+94.2 s is best fit by\na power law function with an exponential high-energy cutoff.\nThe power law index is -0.83 +/- 0.14 and the cutoff energy,\nparameterized as Epeak, is 83 +/- 5 keV.\n\nThe event fluence (10-1000 keV) in this time interval is\n(1.62 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured\nstarting from T0+78 s in the 10-1000 keV band is 8.8 +/- 0.7 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/\"",
  "bibcode": "2025GCN.41411....1D",
  "format": "text/plain"
}