[vsnet-grb-info 23036] LIGO/Virgo S190720a: No counterpart candidates in Fermi-LAT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25135
SUBJECT: LIGO/Virgo S190720a: No counterpart candidates in Fermi-LAT observations
DATE:    19/07/21 09:15:18 GMT
FROM:    Magnus Axelsson at Stockholm U.  <magaxe at kth.se>

M. Axelsson (KTH and Stockholm Univ.) reports on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on July 20, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger S190720a (GCN 25115).

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 ~45% of the LIGO probability region at the time of the trigger (T0 = 2019-07-20 00:08:36.704 UTC), and reached full coverage at T0+4 ks.

We performed a search for a transient counterpart within the observed region of the 90% contour of the LIGO 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 1.4E-10 and 3.9E-09 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Magnus Axelsson (magaxe at kth.se<mailto:magaxe at kth.se>).

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.