GCN Circular 21696

M. Ageron (CPPM/CNRS), B. Baret (APC/CNRS), A. Coleiro (IFIC & APC), D. 
Dornic (CPPM/CNRS), A. Kouchner (APC/Universite Paris Diderot), T.
Pradier (IPHC/Universite de Strasbourg) report on behalf of the ANTARES 
Collaboration:

Using on-line data from the ANTARES detector, we have performed a 
follow-up analysis of the recently reported LIGO/Virgo G299232 event
using the Bayestar-HLV probability map at event time. The ANTARES 
visibility at the time of the alert together with the 50% and 90% contours
of the probability map are shown in: 
https://www.cppm.in2p3.fr/~dornic/events/G299232/250817_visibility2.png 
<https://www.cppm.in2p3.fr/%7Edornic/events/G298389/gw190817_visi.png> 
(gwantares/GW@ANT51). Considering the location probability provided by 
the LIGO collaboration, there is a 42% chance that the GW emitter was in 
the ANTARES field of view.

No up-going muon neutrino candidate events were recorded in the ANTARES 
sky during a +/- 500s time-window centered on the G299232 event
time. The expected number of atmospheric background events in the region 
visible by ANTARES is ~1.1e-2 in the +/- 500s time window. An
extended search during +/- 1 hour gives no up-going neutrino coincidence.

The results of the second analysis covering the full sky as well as an 
estimate of the upper limit on the associated neutrino fluence will be 
sent in a subsequent circular.

ANTARES, being installed in the Mediterranean Deep Sea, is the largest 
neutrino detector in the Northern Hemisphere. It is primarily
sensitive to astrophysical neutrinos in the TeV-PeV energy range.  At 10 
TeV, the median angular resolution for muon neutrinos is below 0.5 degrees.
In the range 1-100 TeV, ANTARES has the best sensitivity to a large 
fraction of the Southern sky.