[vsnet-grb-info 25099] LIGO/Virgo S200224ca: No counterpart candidates in Fermi-LAT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27199
SUBJECT: LIGO/Virgo S200224ca: No counterpart candidates in Fermi-LAT observations
DATE:    20/02/25 10:25:01 GMT
FROM:    Lorenzo Scotton at CNRS/IN2P3/LUPM  <lorenzoscotton at live.it>

M. Crnogorcevic (Univ. of Maryland & NASA/GSFC), L. Scotton (CNRS/IN2P3/LUPM),
N. Di Lalla (Stanford University), M. Axelsson (KTH & Stockholm Univ),
E. Bissaldi (Politecnico & INFN Bari), D. Kocevski (NASA/MSFC),
N. Omodei (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 24, 2020, for possible high-energy (E > 100 MeV) gamma-ray emission in
spatial/temporal coincidence with the LIGO/Virgo trigger S200224ca (GCN 27184).

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 = 2020-02-24 22:22:34.406 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 + 0.5 ks. At that time the
instantaneous coverage was 5% of the LIGO probability map, and reached
almost 100% cumulative coverage at approximately T0 + 6.4 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 + 0.5 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 2.6 e-10 and 4.5 e-10 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is
Lorenzo Scotton (lorenzo.scotton at 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.