GCN Circular 26468

M. Crnogorcevic (Univ. of Maryland & NASA/GSFC), E. Moretti (IFAE,
Barcelona), M. Axelsson (KTH & Stockholm Univ,), E. Bissaldi (Politecnico &
INFN Bari), N. Omodei (Stanford University), M. Arimoto (Kanazawa Univ.)
and F. Longo (University & INFN, Trieste) report on behalf of the Fermi-LAT
Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on
Dec 16, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in
spatial/temporal coincidence with the LIGO/Virgo trigger S191216ap (GCN
26454
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. Fermi-LAT had an instantaneous coverage of ~80% of the LIGO
probability at the time of the trigger (T0 = 2019-12-16 21:33:38.474 UTC),
and reached 100% cumulative coverage after ~4.5 ks.

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. 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 1.8e-10 and 3.1e-09 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Milena Crnogorcevic (
mcrnogor@astro.umd.edu).

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.



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