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GCN Circular 25426

Subject
Fermi GBM-190816: No counterpart candidates in Fermi-LAT observations
Date
2019-08-21T15:25:01Z (5 years ago)
From
Magnus Axelsson at Stockholm U. <magaxe@kth.se>
M. Axelsson (KTH and Stockholm Univ.), F. Longo (Univ. and INFN Trieste), D. Kocevski (NASA/MSFC) and A. Berretta (University and INFN, Perugia) report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on Aug 16, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the sub threshold event LIGO/Virgo and Fermi GBM-190816 (GCN 25406).

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 a time, and "cumulative coverage" as the integral of the instantaneous coverage over time. Fermi-LAT had instantaneous coverage of 75% of the joint GBM and LIGO/Virgo probability region at the time of the trigger (T0 = 2019-08-16 21:22:13.021 UTC) and reached ~100%
coverage around T0+6 ks.

We performed a search for a transient counterpart within the observed region of the 90% contour of the LIGO/Virgo map in a fixed time window from T0 to T0 + 10 ks. No significant sources were found.

We also performed a search which adapted the time interval of the analysis to the exposure of each region of the sky, and no additional excesses were found.

Energy flux upper bounds for the fixed time interval between 100 MeV and 1 GeV for this search vary between 1.3e-10 and 1.4e-9 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Alessandra Berretta (alessandra.berretta@pg.infn.it<mailto:alessandra.berretta@pg.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.
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