GCN Circular 24082
N. Omodei (Stanford Univ.), F. Longo (University and INFN Trieste), M. Arimoto (Kanazawa Univ.), and E. Bissaldi (Politecnico & INFN Bari) report on behalf of the Fermi-LAT Collaboration: We have searched data collected by the Fermi Large Area Telescope (LAT) for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger ST190408an (Singer et al GCN24069). The Fermi Gamma-ray Space Telescope was passing through the South Atlantic Anomaly (SAA) at the time of the trigger (T0 = 2019-04-08 18:18:02.288 UTC). During SAA passages the LAT does not collect data due to the high charged particle background in this region. The LAT resumed data taking upon exiting the SAA at roughly T0 + 1000 s. At that time the instantaneous coverage of the LIGO map was ~5%, and reached 100% cumulative coverage within ~3 ks. We define "instantaneous coverage" as the integral over the region of the LIGO probability map that is within the LAT field of view at a given time, and "cumulative coverage" as the integral of the instantaneous coverage over time. We performed a search for a transient counterpart within the 90% contour of LIGO map in the time window from T0 to T0 + 10 ks, and no significant new sources are found. We also performed a search which adapted the time interval of the analysis to the exposure of each region of the sky. No significant candidate counterpart was found. Energy flux upper bounds between 100 MeV and 100 GeV for this search vary between 2e-10 and 7e-10 [erg/cm^2/s]. The Fermi-LAT point of contact for this event is Elisabetta Bissaldi (Elisabetta.Bissaldi@ba.infn.it). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.