TITLE:   GCN CIRCULAR
NUMBER:  25172
SUBJECT: LIGO/Virgo S190727h: No counterpart candidates in Fermi-LAT observations
DATE:    19/07/27 15:46:46 GMT
FROM:    Milos Kovacevic at INFN Perugia  <Milos.Kovacevic@pg.infn.it>

M. Kovacevic (INFN Perugia), E. Bissaldi (Politecnico and INFN Bari),  
S. Cutini (INFN Perugia) and F. Longo (University and INFN, Trieste)  
report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on
July 27, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in
spatial/temporal coincidence with the LIGO/Virgo trigger S190727h (GCN 25164).

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 ~69% of the LIGO probability region at the  
time of the trigger
(T0 = 2019-07-27 06:03:33.986 UTC), and reached full coverage at T0+5.4 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 1.5E-10 and 7.3E-09 [erg/cm^2/s].

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