[vsnet-grb-info 23099] LIGO/Virgo S190728q: No counterpart candidates in Fermi-LAT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25198
SUBJECT: LIGO/Virgo S190728q: No counterpart candidates in Fermi-LAT observations
DATE:    19/07/28 15:01:03 GMT
FROM:    Milos Kovacevic at INFN Perugia  <Milos.Kovacevic at pg.infn.it>

M. Kovacevic (INFN Perugia), M. Axelsson (KTH and Stockholm Univ.), F.  
Longo (Univ. and INFN, Trieste) and D. Kocevski (NASA/GSFC)
report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on
July 28, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in
spatial/temporal coincidence with the LIGO/Virgo trigger S190728q (GCN 25187).

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.  
Fermi-LAT had
instantaneous coverage of ~58% of the LIGO probability region at the  
time of the trigger
(T0 = 2019-07-28 06:45:10.529 UTC), and reached ~95% coverage around T0+5.8ks.

The remaining area was not observed within 10ks of the burst.

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 2.3E-10 and 2.7E-08 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Milos Kovacevic  
(milos.kovacevic at 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.