GCN Circular 27368

M. Kovacevic (INFN Perugia), M. Ohno (Hiroshima University), M. Axelsson
(KTH & Stockholm Univ),
E. Bissaldi (Politecnico & INFN Bari), D. Kocevski (NASA/MSFC), N. Omodei
(Stanford Univ.), N. Di Lalla (Stanford Univ.) 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
March 11, 2020, for possible high-energy (E > 100 MeV) gamma-ray emission
in
spatial/temporal coincidence with the LIGO/Virgo trigger S200311bg (GCN
27358
Not found
 
 
).

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.

The Fermi Gamma-ray Space Telescope was passing through the South Atlantic
Anomaly (SAA)
at the time of the trigger (T0 = 2020-03-11 11:58:53.398 UTC). During SAA
passages both the LAT
and the Gamma-ray Burst Monitor (GBM) do not collect data due to the high
charged particle
background in this region.

The LAT resumed taking data upon exiting the SAA at roughly T0 + 1.6 ks.

At that time the instantaneous coverage was 100% of the LIGO probability
map, therefore
100% cumulative coverage was reached at that time as well.

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 + 1.6 ks to T0
+ 10 ks.
No significant new sources are 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 8.0e-10 and 1.1e-8 [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.