GCN Circular 20765
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 G275697 event using the initial LIGO bayestar probability map at event time (LVC GCN Circ. 20763). The ANTARES visibility at the time of the alert together with the 90% contour of the probability map are shown in: https://www.cppm.in2p3.fr/~dornic/events/G275697.png (gwantares/ANT@GW). Considering the location probability provided by the LIGO collaboration, there is a 48% chance that the GW emitter was in the ANTARES field of view. No up-going muon neutrino candidate events were recorded within the 90% contour during a +/- 500s time-window centered on the G275697 event time. The expected number of atmospheric background events in the region visible by ANTARES is ~2.0e-3 in the +/- 500s time window. An extended search during +/- 1 hour gives no up-going neutrino coincidence. 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.