{
  "subject": "GRB 091031: Fermi LAT detection of a faint burst",
  "eventId": "GRB 091031",
  "bibcode": "2009GCN.10163....1D",
  "createdOn": 1258065687000,
  "circularId": 10163,
  "submitter": "Francesco de Palma at U of INFN Bari  <francesco.depalma@ba.infn.it>",
  "email": "francesco.depalma@ba.infn.it",
  "body": "F. de Palma (University and INFN Bari), N. Omodei (INFN Pisa), Julie \nMcEnery (NASA/GSFC) and\nV. Vasileiou (NASA GSFC/UMBC) report on behalf of the Fermi LAT team:\n\nAt 12:00:28 (UT) on 31 October 2009 , the Fermi Large Area Telescope \n(LAT) detected gamma rays\nfrom the long GRB 091031, which was triggered and located by the Fermi \nGamma-ray Burst Monitor\n(GBM) (trigger 278683230 / 091031500,GCN 10115). The angle of the GBM \nbest position (RA, Dec=\n70.58, -59.08) with respect to the LAT boresight was ~22 degrees at the \ntime of the trigger,\nwhich is well inside our field of view.\n\nThe Fermi LAT events after the GBM trigger are spatially and temporally \ncorrelated with the\nemission measured by GBM. In the time interval T0-T0+100s using \nlikelihood methods\non photons above 100 MeV this burst has a significance of more than 3 \nsigma; using counting\nmethods the significance is well over 6 sigma in the full energy band \n(20 MeV - 300 GeV).\nMore than 30 photons above 100 Mev and 2 photons above 1 GeV were \nobserved in the same\ntime interval in an energy dependent ROI centered on the GBM position.\nThe best LAT on-ground localization is found to be (RA, Dec = 71.7, \n-57.5) with a 90%\ncontainment radius of 0.3 deg (statistical; 68% containment radius: 0.2 \ndeg, preliminary\nsystematic error is less than 0.1 deg) which is consistent with the GBM \nlocalization.\n\nFurther analysis is ongoing.\n\nThe point of contact for this burst is\nFrancesco de Palma : francesco.depalma@ba.infn.it\n\nThe Fermi LAT is a pair conversion telescope designed to cover the \nenergy band from 20 MeV to\ngreater than 300 GeV. It is the product of an international \ncollaboration between NASA and DOE\nin the U.S. and many scientific institutions across France, Italy, Japan \nand Sweden.\n\nThis message can be cited."
}