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.