A nearby FR I type radio galaxy 3C 120 as a possible PeV neutrino emitter

Abstract

Although connections between flaring blazars and some IceCube neutrinos have been established, the dominant sources for the bulk extragalactic neutrino emissions are still unclear and one widely suggested candidate is a population of radio galaxies. Because of their relatively low $\gamma$-ray radiation luminosities ($L_\gamma$), it is rather challenging to confirm such a hypothesis with the neutrino/GeV $\gamma$-ray flare association. Here we report on the search for the GeV $\gamma$-ray counterpart of the neutrino IC-180213A and show that the nearby ($z$ = 0.03) broad line radio galaxy 3C 120 is the only known co-spatial GeV $\gamma$-ray source in a half-year epoch around the neutrino detection. An intense $\gamma$-ray flare, the second strongest one among the entire 16-year period, is temporally coincident with the detection of IC-180213A. Moreover, accompanying optical brightenings in $g$-band and $V$-band are observed. We also find that the IC-180213A / 3C 120 association follows the $L_\gamma$-$D_{L}^{2}$ correlation for the neutrino sources (candidates), including NGC 1068 and some blazars. These facts suggest that 3C 120 is a candidate for emitting high-energy neutrinos and may offer an initial evidence for the radio galaxy origin of some PeV neutrinos.