Searches for coincident Gravitational Waves and High-Energy Neutrinos from the KM3NeT and ANTARES telescopes during O3

Various models predict that gravitational-wave sources produce high-energy neutrinos. Among them are compact binary coalescences with at least one neutron star, but also core-collapse supernovae or accretion disk instabilities. Two different analyses are presented, combining data from the LIGO and Virgo gravitational-wave detectors with those from the ANTARES and ORCA neutrino telescopes observed during the third observing run of LIGO-Virgo. In the first analysis, selected high-energy neutrino candidates were used as triggers to search for gravitational-wave candidates. In the second analysis, a search was conducted for potential spatial and temporal coincidences between subthreshold high-energy neutrino candidate events and subthreshold gravitational-wave candidates emitted by compact binary coalescence systems. In both searches, no significant coincidences were found. Upper limits on the rate of sources emitting both high-energy neutrinos and gravitational waves are presented. In particular, with the joint search, a joint source rate density upper limit of $8.8\times {10}^2\mathrm{G}\mathrm{p}{\mathrm{c}}^{-3}\mathrm{y}{\mathrm{r}}^{-1}$ was found for a typical binary neutron star coalescence with a GW emitted energy of ${10}^{-1}{\mathrm{M}}_{\odot }{\mathrm{c}}^2$ and an isotropic energy emitted in neutrinos of ${10}^{51}$erg.