{
  "bibcode": "2022GCN.32642....1L",
  "body": "S. Lesage (UAH), P. Veres (UAH), O.J. Roberts (USRA),\nE. Burns (LSU), and E. Bissaldi (Politecnico and INFN Bari)\nreport on behalf of the Fermi GBM Team:\n\n\"At 13:16:59.99 UT on 09 October 2022, the Fermi Gamma-Ray Burst Monitor\ntriggered and located GRB 221009A (trigger 687014224/221009553) which\nwas also detected by Swift-BAT (S. Dichiara, et al. 2022, GCN 32632;\nJ. A. Kennea, et al. 2022, GCN 32635), Fermi-LAT (E. Bissaldi et al. 2022,\nGCN 32637), INTEGRAL (SPI-ACS), Konus-Wind, and triangulated by IPN\n(D. Svinkin et al. 2022, GCN 32641). The GBM on-ground location (GCN 32636)\nis\nconsistent with the Swift-BAT and Fermi-LAT locations and the IPN\nlocalization.\n\nThe angle from the Fermi LAT boresight is 73 degrees.\n\nThe GBM light curve consists of two emission episodes, a single isolated\npeak\nfollowed by a longer, extremely bright, multi-pulsed emission episode with\na duration (T90) of about 327 s (10-1000 keV).\n\nThe time-averaged spectrum for the first emission episode\nfrom T0-0.0 to T0+43.4 s is best fit by\na power law function with an exponential high-energy cutoff.\nThe power law index is -1.70 +/- 0.02 and the cutoff energy,\nparameterized as Epeak, is 375 +/- 87 keV.\nThe event fluence (10-1000 keV) in this time interval is\n(2.12 +/- 0.05)E-05 erg/cm^2.\n\nDue to the brightness of the second emission episode, the likelihood of\npulse pile-up and other systematic effects are very high and no single\nspectral model provides an adequate fit in this preliminary analysis.\nThe event fluence (10-1000 keV) from T0+175 to T0+1458 s\nis on the order of (2.912 +/- 0.001)E-02 erg/cm^2.\nThe 1.024 sec peak photon flux measured\nstarting from T0+238.8 s in the 10-1000 keV band\nis on the order of 2385 +/- 3 ph/s/cm^2,\nmaking this the most intense and fluent GRB detected by Fermi GBM.\n\nFurther analysis is being performed.\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\nPage:\nhttps://fermi.gsfc.nasa.gov/ssc/data/access/gbm/\"",
  "circularId": 32642,
  "createdOn": 1665374681000,
  "email": "sjl0014@uah.edu",
  "subject": "GRB 221009A: Fermi GBM observation",
  "submitter": "Stephen Lesage at Fermi-GBM Team  <sjl0014@uah.edu>",
  "eventId": "GRB 221009A"
}