Angular correlation of cosmic neutrinos with ultrahigh-energy cosmic rays and implications for their sources

Cosmic neutrino events detected by the IceCube Neutrino Observatory with energy greater than or similar to 30 TeV have poor angular resolutions to reveal their origin. Ultrahigh-energy cosmic rays (UHECRs), with better angular resolutions at > 60 EeV energies, can be used to check if the same astrophysical sources are responsible for producing both neutrinos and UHECRs. We test this hypothesis, with statistical methods which emphasize invariant quantities, by using data from the Pierre Auger Observatory, Telescope Array and past cosmic-ray experiments. We find that the arrival directions of the cosmic neutrinos are correlated with >= 100 EeV UHECR arrival directions at confidence level approximate to 90%. The strength of the correlation decreases with decreasing UHECR energy and no correlation exists at energy similar to 60 EeV. A search in astrophysical databases within 3 degrees of the arrival directions of UHECRs with energy > 100 EeV, that are correlated with the IceCube cosmic neutrinos, resulted in 18 sources from the Swift-BAT X-ray catalog with redshift z <= 0.06. We also found 3 objects in the Kuhr catalog of radio sources using the same criteria. The sources are dominantly Seyfert galaxies with Cygnus A being the most prominent member. We calculate the required neutrino and UHECR fluxes to produce the observed correlated events, and estimate the corresponding neutrino luminosity (25 TeV-2.2 PeV) and cosmic-ray luminosity (500 TeV-180 EeV), assuming the sources are the ones we found in the Swift-BAT and Kuhr catalogs. We compare these luminosities with the X-ray luminosity of the corresponding sources and discuss possibilities of accelerating protons to greater than or similar to 100 EeV and produce neutrinos in these sources.