[vsnet-grb-info 23431] LIGO/Virgo S190828j: No counterpart candidates in Fermi-LAT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25530
SUBJECT: LIGO/Virgo S190828j: No counterpart candidates in Fermi-LAT observations
DATE:    19/08/28 22:43:12 GMT
FROM:    Frederic Piron at CNRS/IN2P3/LUPM  <piron at in2p3.fr>

F. Piron (CNRS/IN2P3/LUPM), N. Omodei (Stanford Univ.), F. Longo (Univ. 
and INFN Trieste), M. Arimoto (Kanazawa Univ.), D. Kocevski (NASA/MSFC), 
M. Axelsson (KTH and Stockholm Univ.) and E. Bissaldi (Politecnico and 
INFN Bari) report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) 
on Aug 28, 2019, for possible high-energy (E > 100 MeV) gamma-ray 
emission in spatial/temporal coincidence with the LIGO/Virgo trigger 
S190828j (GCN 25497).

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 a null instantaneous coverage of the 
LIGO probability region at the time of the trigger (T0 = 2019-08-28 
06:34:05.756UTC), and reached ~52% cumulative coverage after 10 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 4.3e-10 and 8.5e-8 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Frederic Piron 
(piron at in2p3.fr).

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.