[vsnet-grb-info 22540] LIGO/Virgo S190521g: No candidate counterpart in Fermi-LAT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24639
SUBJECT: LIGO/Virgo S190521g: No candidate counterpart in Fermi-LAT observations
DATE:    19/05/21 13:01:51 GMT
FROM:    Magnus Axelsson at Stockholm U.  <magaxe at kth.se>

M. Axelsson (KTH and Stockholm Univ.), D. Tak (Univ. of Maryland) 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) on May 21, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger S190521g (GCN 24621).

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 ~15% of the LIGO probability at the time of the trigger (T0 = 2019-05-21 03:02:29.447 UTC), and reached 100% cumulative coverage after ~5.5 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 1.5e-10 and 2.2e-09 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Donggeun Tak (takdg123 at umd.edu<mailto:takdg123 at umd.edu>).

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.