{
  "bibcode": "2017GCN.21528....1G",
  "body": "A. Goldstein (USRA), P. Veres (UAH), and A. von Kienlin (MPE) report on\nbehalf of the GBM-LIGO Group:\nL. Blackburn (CfA), M. S. Briggs (UAH), J. Broida (Carleton College), E.\nBurns (NASA/GSFC), J. Camp (NASA/GSFC), T. Dal Canton (NASA/GSFC), N.\nChristensen (Carleton College), V. Connaughton (USRA), R. Hamburg (UAH), C.\nM. Hui (NASA/MSFC), P. Jenke (UAH), D. Kocevski (NASA/MSFC), N. Leroy\n(LAL), T. Littenberg (NASA/MSFC), J. McEnery (NASA/GSFC), R. Preece (UAH),\nJ. Racusin (NASA/GSFC), P. Shawhan (UMD), K. Siellez (GATech), L. Singer\n(NASA/GSFC), J. Veitch (Glasgow), C. Wilson-Hodge (NASA/MSFC)\n\n\nThe GBM trigger (Connaughton et al., LVC GCN 21506), which we determine to\nbe a short GRB, occurred about 2 minutes before Fermi entered the South\nAtlantic Anomaly. To estimate the False Alarm Rate (FAR) of a chance\ncoincident short GRB without using spatial information, we estimate the\nrate of short GRBs (defined as t90 <= 2 s) triggered by GBM.  GBM has a\ntotal of 351 triggered short GRBs over an estimated triggering livetime of\n3.23e8 s. This results in a FAR of one per 10.7 days. A simple estimate of\nthe False Alarm Probability using only the temporal information of the two\nsignals is 2.2e-6 (~4.5 sigma).\n\nThe initial public report of the GRB (von Kienlin et al., GCN 21520)\ncontained the spectral information using the maximum of the GBM\nlocalization posterior. Using the maximum of the updated LIGO/Virgo\nlocalization posterior (LVC, LVC GCN 21513), which is consistent with the\nGBM localization, we report the updated preliminary spectral information.\n\nThe estimated GRB duration is ~ 2 s and is best fit by a power-law function\nwith an exponential high-energy cutoff from T0-0.75 to T0+1.25 s.  The\npower-law index is -0.88 +/- 0.44 and the cutoff energy, parametrized as\nEpeak, is 128.0 +/- 48.7 keV. The event fluence (10-1000 keV) in this time\ninterval is (2.2 +/- 0.5)e-7 erg/cm^2, which we estimate to be near the\n58th percentile of GBM-triggered short GRB fluences. The 64 ms peak photon\nflux estimated starting at T0 is 3.6 +/- 1.1 ph/s/cm^2 (10-1000 keV).  The\ncorresponding spectrum over this peak flux interval is fit by an\nexponential high-energy power law with index = -0.29 +/- 1.01 and Epeak =\n124.2 +/- 52.6 keV.  The event peak energy flux (10-1000 keV) is (7.3 +/-\n2.4)e-7 erg/s/cm^2.\n\nUsing this spectral information and the distance information provided by\nthe LVC (40 +/- 8 Mpc) we estimate that the isotropic energy release in\ngamma-rays, Eiso ~ 4.3e46 erg in the 1 keV-10 MeV energy range and the\nisotropic peak luminosity, Liso ~1.4e47 erg/s.\n\nThese results are preliminary and may be updated with further analysis.",
  "circularId": 21528,
  "createdOn": 1503016572000,
  "email": "adam.michael.goldstein@gmail.com",
  "subject": "LIGO/Virgo G298048 - Update on Fermi/GBM GRB 170817A Analysis",
  "submitter": "Adam Goldstein at Fermi/GBM  <adam.michael.goldstein@gmail.com>",
  "eventId": "LIGO/Virgo G298048"
}