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Neutrino Bursts from Fanaroff-Riley I Radio Galaxies

On the basis of existing observations (at the 4.5 σlevel) of TeV gamma-ray outbursts from the Fanaroff-Riley I (FRI) radio galaxy Centaurus A, we estimate the accompanying neutrino flux in a scenario where both photons and neutrinos emerge from pion decay. We find a neutrino flux on Earth dF_ν/dE_ν= 4.5\times 10^{-11} (E_ν/TeV)^{-2} TeV^{-1} cm^{-2} s^{-1}, equally spread in flavor as a result of maximal mixing. Such a flux will trigger at the IceCube facility about 10 showers/burst, with negligible background from atmospheric muons, and primary neutrino energies in excess of 100 TeV. The only other FRI radio galaxy observed in the TeV photon energy range at the 4σlevel is M87. The burst nature of this activity is not established; however, we show that the intrinsic neutrino luminosity during the active period is the same as the Centaurus A burst. On the assumption that Centaurus A typifies the FRI population, we show that IceCube should collect 10 showers (all neutrino flavors) in 3 years, attaining a 95% CL sensitivity to the diffuse neutrino flux from FRI radio galaxies in one year of observation.