TITLE: GCN CIRCULAR NUMBER: 30971 SUBJECT: IceCube-211023A: No neutrino counterpart detected with ANTARES DATE: 21/10/24 12:37:26 GMT FROM: Antoine Kouchner at ANTARES Collaboration <kouchner@apc.in2p3.fr> Alexis Coleiro (APC/Universite de Paris) and Damien Dornic (CPPM/CNRS) on behalf of the ANTARES Collaboration. Using data from the ANTARES detector, we have performed a follow-up analysis of the recently reported bronze track event IceCube-211023A (GCN #30957 <https://gcn.gsfc.nasa.gov/gcn3/30957.gcn3>). The reconstructed origin was slightly above the horizon for ANTARES at the time of the alert (+0.8 degrees). No horizontal muon neutrino candidate events were recorded within 90% error box of the IceCube event during a +/- 1h time-window centered on the IceCube event time, and over which the potential source remained visible half of the time. This leads to a preliminary 90% confidence level upper limit on the muon-neutrino fluence from a point source of about 12 GeV.cm^-2 over the energy range 3 TeV – 3 PeV (the range corresponding to 5-95% of the detectable flux) for an E^-2 power-law spectrum, and 48 GeV.cm^-2 (600 GeV - 300 TeV) for an E^-2.5 spectrum. A search over an extended time window of +/- 1 day has also yielded no detection (51% visibility). ANTARES <http://antares.in2p3.fr/> is the largest undersea neutrino detector (Mediterranean Sea) and it is primarily sensitive to astrophysical neutrinos in the TeV-PeV energy range. At 10 TeV, the median angular resolution for muon neutrinos is about 0.5 degrees. In the range 1-100 TeV ANTARES has a competitive sensitivity to this position in the sky.