{
  "bibcode": "2019GCN.24082....1O",
  "body": "N. Omodei (Stanford Univ.), F. Longo (University and INFN Trieste), M.\nArimoto (Kanazawa Univ.),\nand E. Bissaldi (Politecnico & INFN Bari) report on behalf of the\nFermi-LAT Collaboration:\n\nWe have searched data collected by the Fermi Large Area Telescope (LAT)\nfor possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal\ncoincidence with the LIGO/Virgo trigger ST190408an (Singer et al GCN24069).\n\nThe Fermi Gamma-ray Space Telescope was passing through the South Atlantic\nAnomaly (SAA) at the time of the trigger (T0 = 2019-04-08 18:18:02.288 UTC).\nDuring SAA passages the LAT does not collect data due to the high\ncharged particle background in this region.\nThe LAT resumed data taking upon exiting the SAA at roughly T0 + 1000 s.\nAt that time the instantaneous coverage of the LIGO map was ~5%, and reached\n100% cumulative coverage within ~3 ks. We define \"instantaneous coverage\"\nas the integral over the region of the LIGO probability map that is\nwithin the LAT\nfield of view at a given time, and \"cumulative coverage\" as the integral of the\ninstantaneous coverage over time.\n\nWe performed a search for a transient counterpart within the 90% contour of\nLIGO map in the time window from T0 to T0 + 10 ks, and no significant\nnew sources are found.\n\nWe also performed a search which adapted the time interval of the analysis to\nthe exposure of each region of the sky. No significant candidate counterpart\nwas found.\n\nEnergy flux upper bounds between 100 MeV and 100 GeV for this search vary\nbetween 2e-10 and 7e-10 [erg/cm^2/s].\n\nThe Fermi-LAT point of contact for this event is\nElisabetta Bissaldi (Elisabetta.Bissaldi@ba.infn.it).\n\nThe Fermi-LAT is a pair conversion telescope designed to cover\nthe energy band from 20 MeV to greater than 300 GeV\nIt is the product of an international collaboration between\nNASA and DOE in the U.S. and many scientific institutions\nacross France, Italy, Japan and Sweden.",
  "circularId": 24082,
  "createdOn": 1554826950000,
  "email": "arimoto@hp.phys.titech.ac.jp",
  "subject": "LIGO/Virgo ST190408an: Fermi-LAT search for a high-energy gamma-ray counterpart",
  "submitter": "Makoto Arimoto at Tokyo Inst of Tech  <arimoto@hp.phys.titech.ac.jp>"
}