KM3-230213A: An Ultra-High Energy Neutrino from a Year-Long Astrophysical Transient
arXiv:2502.12986
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 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 yr with muon neutrino flux $F \approx 3\times 10^{-10}(1\mbox{ yr }/ T)$ erg cm s. Constraints on the neutrino spectrum indicate that the protons responsible for the neutrino emission have a very hard spectrum in the 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 yr.
6 pages, 1 figure, prepared for submission to PRD