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

¹ Department of Physics and Astronomy, College of Physics, Guizhou University, Guiyang 550025, People’s Republic of China
² Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, People’s Republic of China
³ School of Astronomy and Space Science, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China

^⋆ Corresponding authors: nhliao@gzu.edu.cn; yzfan@pmo.ac.cn

Received: 25 November 2024
Accepted: 8 August 2025

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 γ-ray radiation luminosities (L_γ), it is rather challenging to confirm such a hypothesis with the association between an incoming neutrino and a GeV γ-ray flare. Here, we report on the search for the GeV γ-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 γ-ray source in a half-year epoch around the neutrino detection. An intense γ-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 the g band and V band are observed. We also find that the 3C 120, as a possible neutrino emitter, follows the L_γ-D_L² 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 initial evidence of the radio galaxy origin of some PeV neutrinos.