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arXiv · 2502.12986

KM3-230213A: An Ultra-High Energy Neutrino from a Year-Long Astrophysical Transient

Andrii Neronov·Foteini Oikonomou·Dmitri Semikoz
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Abstract

The Km3NET collaboration has recently reported the detection of a neutrino event with energy in excess of 100 PeV. This detection is in 2.5-3$σ$ tension with the upper limit on the neutrino flux at this energy imposed by IceCube and the Pierre Auger Observatory, if the event is considered part of the diffuse all-sky neutrino flux. We explore an alternative possibility that the event originates from a flare of an isolated source. We show that the data of Km3NET, IceCube and the Pierre Auger Observatory are consistent with the possibility of a source flare of duration $T \lesssim 2$ yr with muon neutrino flux $F \approx 3\times 10^{-10}(1\mbox{ yr }/ T)$ erg cm$^{-2}$ s$^{-1}$. Constraints on the neutrino spectrum indicate that the protons responsible for the neutrino emission have a very hard spectrum in the $E_p\gtrsim 10^{19}$ eV energy range, or otherwise that the neutrinos are produced by photohadronic interactions with infrared photons. The all-sky rate of similar neutrino flaring sources is constrained to be $R\lesssim 0.4/$ yr.

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Andrii Neronov, Foteini Oikonomou, Dmitri Semikoz. 2025-02-18. KM3-230213A: An Ultra-High Energy Neutrino from a Year-Long Astrophysical Transient. https://arxiv.org/abs/2502.12986

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