GCN Circular 26654

F. Longo (University and INFN, Trieste), D. Kocevski (NASA/MSFC), M.
Axelsson (KTH & Stockholm Univ.)
and N. Omodei (Stanford Univ.) report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on
January 5th, 2020, for possible high-energy (E > 100 MeV) gamma-ray emission in
spatial/temporal coincidence with the LIGO/Virgo sub threshold trigger
S200105ae
(GCN 26640
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 ).

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
an instantaneous coverage of ~40% of the LIGO probability at the time
of the trigger
(T0 =2020-01-05 16:24:26 UTC), and reached ~75% cumulative coverage after about
5 ks. The remaining area was not observed within 10 ks following the
trigger time of
the event.

We performed a search for a transient counterpart within the observed region of
the 90% contour of LIGO map in a fixed time window from T0 to T0 + 10 ks.
One significant excess (with TS>25) was found at R.A., Dec. = 215.6,
32.3, but it is likely
associated with the known and currently active source OQ 334 (lies
within the 90%
uncertainty region).

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 1.1e-10 and 3.5e-07 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is
F.Longo (francesco.longo@ts.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.