{
  "bibcode": "2022GCN.32658....1P",
  "body": "GRB 221009A: Fermi-LAT refined analysis\n\nR. Pillera (Politecnico and INFN Bari), E Bissaldi (Politecnico and INFN \nBari),\nN. Omodei (Stanford Univ.), G. La Mura (LIP, Portugal),\nF. Longo (University and INFN Trieste) report on behalf of the Fermi-LAT \nteam:\n\n\nWe report updated observations of GRB 221009A which was detected by\nSwift (Kennea et al. GCN #32635), Fermi-GBM (Veres et al. GCN #32636,\nLesage et al. GCN #32642), Fermi-LAT (Bissaldi et al. GCN #32637),\nand the IPN (Svinkin et al. GCN #32641).\n\nGRB 221009A triggered Fermi-GBM on October 10, 2022, at 13:16:59.99 UT\n(trigger 687014224/221009553), about 1 hour earlier with respect\nto the Swift trigger,  which was reported as a new bright\nhard X-ray and optical transient and tentatively classified\nas Swift J1913.1+1946 (Dichiara et al., GCN 32632).\nPrompt GCN notices from Fermi-GBM were not distributed\ndue to problems with the real-time downlink from TDRS,\ntherefore no automatic Fermi-LAT GRB pipelines were triggered\nby the GBM event.\n\nUsing LAT events with E>100 MeV between T0+200 s and T0+800 s,\nwe find a LAT localization of\n\nRA = 288.282, Dec = 19.495,\n\nwith a 90% containment radius of 0.027 degrees (statistical only).\n\nThe LAT lightcurve shows a bright structured emission episode\nwhich is temporally coincident with the GBM main emission episode\nstarting at T0+200s.\nThe 100 MeV - 1 GeV photon flux in the time interval 200-800 s after\nthe GBM trigger is (6.2 +/- 0.4)E-03 ph/cm2/s.\nThe estimated photon index above 100 MeV is -1.87 +/- 0.04.\n\n From a preliminary analysis, the LAT emission\nis extending for about 25ks post GBM trigger.\nThe highest-energy photon is 99.3 GeV (with a probability of 99.2%)\nwhich is observed 240 seconds after the GBM trigger.\nThis represents the highest GRB photon energy\never detected by Fermi-LAT (the previous record holder being\na 95 GeV event from GRB 130427A).\n\nThe Fermi-LAT point of contact for this burst is\nElisabetta Bissaldi (elisabetta.bissaldi@ba.infn.it).\n\nThe Fermi-LAT is a pair conversion telescope designed to\ncover the energy band from 20 MeV to greater than 300 GeV.\nIt is the product of an international collaboration\nbetween NASA and DOE in the U.S. and many scientific\ninstitutions across France, Italy, Japan and Sweden.",
  "circularId": 32658,
  "createdOn": 1665409366000,
  "email": "roberta.pillera@ba.infn.it",
  "subject": "GRB 221009A: Fermi-LAT refined analysis",
  "submitter": "Roberta Pillera at Politecnico and INFN Bari  <roberta.pillera@ba.infn.it>",
  "eventId": "GRB 221009A"
}