{
  "submittedHow": "web",
  "circularId": 35044,
  "subject": " GRB 231115A:  Fermi Observations of a probable Magnetar Giant Flare from M82",
  "bibcode": "2023GCN.35044....1D",
  "createdOn": 1700081445486,
  "submitter": "Sarah Dalessi at UAH <sd0104@uah.edu>",
  "body": "S. Dalessi (UAH), O.J. Roberts (USRA/NASA-MSFC), P. Veres (UAH) and C. Meegan (UAH) report on behalf of\nthe Fermi Gamma-ray Burst Monitor Team:\n\n\"At 15:36:21.20 UT on 15 November 2023, the Fermi Gamma-ray Burst Monitor (GBM)\ntriggered and located GRB 231115A (trigger 721755386/231115650).\nwhich was also detected by Integral (P. D'Avanzo et al. 2023, GCN 35036 and S.Mereghetti et al. 2023, GCN 35037).\nThe Fermi GBM Final Real-time Localization is reported in GCN 35035 and is consistent with the Integral position.\n\nThe angle from the Fermi LAT boresight is 38 degrees.\n\nThe GBM light curve single peak with a duration (T90)\nof about 0.03 s (50-300 keV). The time-averaged spectrum\nfrom T0-0.02 to T0+0.02 s is best fit by\na power law function with an exponential high-energy cutoff.\nThe power law index is 0.5 +/- 0.2 and the cutoff energy,\nparameterized as Epeak, is 580 +/- 60 keV.\n\nThe event fluence (10-1000 keV) in this time interval is\n(6.3 +/- 0.4)E-07 erg/cm^2. The 64-ms peak photon flux measured\nstarting from T0+0.0 s in the 10-1000 keV band is 11 +/- 1 ph/s/cm^2.\n\nUsing the distance to M82 of 3.5 Mpc (P. D'Avanzo et al. 2023, GCN 35036), we derive an Eiso of 1.4e45 ergs and Liso of 1.9e46 erg s-1 (64 ms, 1-10,000 keV). This with the rise time of ~2 ms, hard spectral slope and soft-hard-soft spectral evolution of the event, are consistent with an MGF origin.\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/\"",
  "eventId": "GRB 231115A"
}