GCN Circular 26357

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

We have searched data collected by the Fermi Large Area Telescope (LAT) on
December 4th, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in
spatial/temporal coincidence with the LIGO/Virgo trigger S191204r (GCN 26334
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 = 2019-12-04 17:15:26 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 + 1.3 ks. At that time no
part of the LIGO probability map was observable. The region entered the LAT field
of view around T0 + 2 ks, and 100% cumulative coverage was reached after ~7.3 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 + 1.3 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
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 1e-10 and 5e-10 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is
Lorenzo Scotton (lorenzo.scotton@lupm.in2p3.fr<mailto:lorenzo.scotton@lupm.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.