{
  "bibcode": "2020GCN.27199....1C",
  "body": "M. Crnogorcevic (Univ. of Maryland & NASA/GSFC), L. Scotton (CNRS/IN2P3/LUPM),\r\nN. Di Lalla (Stanford University), M. Axelsson (KTH & Stockholm Univ),\r\nE. Bissaldi (Politecnico & INFN Bari), D. Kocevski (NASA/MSFC),\r\nN. Omodei (Stanford Univ.) and F. Longo (University and INFN, Trieste)\r\n\r\nreport on behalf of the Fermi-LAT Collaboration:\r\n\r\nWe have searched data collected by the Fermi Large Area Telescope (LAT) on\r\nFebruary 24, 2020, for possible high-energy (E > 100 MeV) gamma-ray emission in\r\nspatial/temporal coincidence with the LIGO/Virgo trigger S200224ca (GCN 27184).\r\n\r\nWe define \"instantaneous coverage\" as the integral over the region of the LIGO\r\nprobability map that is within the LAT field of view at a given time, and \"cumulative\r\ncoverage\" as the integral of the instantaneous coverage over time.\r\n\r\nThe Fermi Gamma-ray Space Telescope was passing through the South Atlantic\r\nAnomaly (SAA) at the time of the trigger (T0 = 2020-02-24 22:22:34.406 UTC).\r\nDuring SAA passages both the LAT and the Gamma-ray Burst Monitor (GBM) do not\r\ncollect data due to the high charged particle background in this region. The LAT\r\nresumed taking data upon exiting the SAA at roughly T0 + 0.5 ks. At that time the\r\ninstantaneous coverage was 5% of the LIGO probability map, and reached\r\nalmost 100% cumulative coverage at approximately T0 + 6.4 ks.\r\n\r\nWe performed a search for a transient counterpart within  the observed region of\r\nthe 90% contour of the LIGO map in a fixed time window from T0 + 0.5 ks to T0 + 10 ks.\r\nNo significant new sources are found.\r\n\r\nWe also performed a search which adapted the time interval of the analysis to the\r\nthe exposure of each region of the sky, and no additional excesses were found.\r\n\r\nEnergy flux upper bounds for the fixed time interval between 100 MeV and 1 GeV\r\nfor this search vary between 2.6 e-10 and 4.5 e-10 [erg/cm^2/s].\r\n\r\nThe Fermi-LAT point of contact for this event is\r\nLorenzo Scotton (lorenzo.scotton@lupm.in2p3.fr).\r\n\r\nThe Fermi-LAT is a pair conversion telescope designed to cover\r\nthe energy band from 20 MeV to greater than 300 GeV.\r\nIt is the product of an international collaboration between\r\nNASA and DOE in the U.S. and many scientific institutions\r\nacross France, Italy, Japan and Sweden.",
  "circularId": 27199,
  "createdOn": 1582626301000,
  "email": "lorenzoscotton@live.it",
  "subject": "LIGO/Virgo S200224ca: No counterpart candidates in Fermi-LAT observations",
  "submitter": "Lorenzo Scotton at CNRS/IN2P3/LUPM  <lorenzoscotton@live.it>",
  "eventId": "LIGO/Virgo S200224ca"
}