The blazar PKS 0605-085 as the origin of the KM3-230213A ultra high energy neutrino event

Abstract

The KM3Net Collaboration has recently reported on the observation of a remarkable event KM3-230213A that could have been produced by an ultra high energy cosmic neutrino. The origin of this event is still unclear. In particular, the cosmogenic neutrino scenario is not favoured due to the non-observation of a similar event by the IceCube detector, and most galactic scenarios are disfavoured as well. We show that the blazar PKS 0605-085 is a viable source of the KM3-230213A event. In particular, even though this blazar is located at 2.4$^{\circ}$ from the KM3-230213A event, the association between the blazar and the event is not unlikely due to a sizable direction systematic uncertainty of $\approx 1.5^{\circ}$ reported by the KM3Net Collaboration. Furthermore, we show that the observation of a $\approx$72 PeV neutrino from PKS 0605-085 is entirely possible given that a $\approx$7.5 PeV neutrino could have been observed from another blazar TXS 0506+056. Finally, we consider $\gamma$-ray constraints on the number of observable neutrino events and show that for the case of the external photon field production mechanism these constraints could be relaxed due to the often-neglected effect of the isotropisation of the hadronically-produced electrons in the magnetic field of the blob. We encourage further multi-wavelength observations of the blazar PKS 0605-085.