2025MNRAS.544.4217F

The production sites of high-energy astrophysical neutrinos remain uncertain, though growing evidence suggests a connection to relativistic jets in active galactic nuclei (AGNs). We present a detailed analysis of the recent PeV neutrino event KM3-230213A reported by the KM3NeT collaboration, aiming to constrain the physical conditions of its source. Assuming proton acceleration at shocks, we derive the properties of the proton distribution and the energetics required to explain the neutrino emission. Using contemporaneous multiwavelength observations of three AGN flaring candidates within the error region, we examine the plausibility of each of them as the possible counterpart. Our results favour PMN J0606-0724, which exhibits a prominent radio flare coincident with the neutrino arrival. In this framework, the red-giant interaction remains the key driver of baryon injection and shock acceleration, while the dominant external photon field sets the neutrino energy scale: photospheric photons from the red giant yield ∼1-10 PeV neutrinos, whereas the ∼220 PeV event KM3-230213A is more naturally produced through interactions with colder infrared photons from the dusty torus.