Searches for ultrahigh-energy neutrinos from gravitational wave events with the Pierre Auger Observatory

With the advent of the multi-messenger astronomy era, neutrinos open a unique window to the Universe allowing one to relate the most violent phenomena with the production and origin of the highest energy cosmic rays at distances beyond the GZK horizon. Neutrinos with E > 0.1 EeV of all flavors can be detected with the Surface Detector array of the Pierre Auger Observatory by means of their interaction in the atmosphere (downward-going ) or in the Earth crust (Earth-skimming ). The Pierre Auger Collaboration has searched for neutrino candidates in coincidence with gravitational wave events detected by LIGO/Virgo. Up to the present moment no neutrino candidates were found in any of these searches, which allows us to put competitive limits on the energy radiated in ultra-high energy neutrinos. The most stringent limits to the neutrino spectral fluence arise from the binary neutron star merger event GW170817 at a D_s ∼ 40 Mpc. The non-detection of neutrinos from this event is compatible with the predictions of a short GRB observed at a large off-axis angle. (paper)