TITLE:   GCN CIRCULAR
NUMBER:  27143
SUBJECT: LIGO/Virgo S200219ac: No counterpart candidates in Fermi-LAT observations
DATE:    20/02/19 20:58:12 GMT
FROM:    Feraol Dirirsa at U of Johannesburg/Fermi-LAT  <fdirirsa@uj.ac.za>

F. Dirirsa (Univ. of Johannesburg), 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
February 19, 2020, for possible high-energy (E > 100 MeV) gamma-ray emission in
spatial/temporal coincidence with the LIGO/Virgo trigger S200219ac (GCN 27130).

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
no coverage at the time of the trigger (T0 = 2020-02-19 09:44:15.195 UTC), and reached 87% cumulative coverage
after ~2.5 ks. The remaining region 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.
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 1.4e-10 and 7.8e-08 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is
Feraol Dirirsa (fdirirsa@uj.ac.za).

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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