Blazars as a Potential Origin of the KM3-230213A Event

TL;DR

The paper investigates whether a population of blazars can account for the KM3NeT/ARCA-detected ultra-high-energy neutrino KM3-230213A, without overshooting the Fermi-LAT extragalactic gamma-ray background. It employs the AM3 one-zone blazar jet model to predict single-blazar gamma-ray and neutrino spectra and couples this with the Fermi-LAT gamma-ray luminosity function to estimate the diffuse blazar flux. A joint likelihood with KM3NeT/ARCA and IceCube exposures, plus a gamma-ray safety penalty from the EGB, yields best-fit parameters $\tilde{\eta}\approx 10$ and $\tilde{\alpha_p}\approx 1.8$, indicating blazars can plausibly explain the event under gamma constraints; KM3NeT-only fits push $\eta$ higher (≈$10^3$), suggesting a need for more luminous sources to fully account for the event. Overall, the study supports blazars as a viable contributor to ultra-high-energy neutrinos and provides quantitative limits on jet loading and proton spectra within a population context, reinforcing the value of multimessenger modeling for extreme-energy phenomena.

Abstract

The KM3NeT collaboration has reported the detection of the highest energy neutrino event observed to date. The energy of the event is of the order of 220 PeV hinting towards a neutrino flux at the highest energies. In this article, the potential blazar origin for this event is explored. The publicly available Astro-Multimessenger Modeling software is used to model the blazar gamma-ray and neutrino fluxes. It is concluded that a population of blazars could produce the diffuse flux compatible with the observation of the ultra-high energy event detected by the KM3NeT/ARCA detector. At the same time, the gamma-ray flux produced by such a population of blazars is consistent with the diffuse gamma-ray flux measured by the Fermi Large Area Telescope.

Figures (7)

• Figure 1: Differential luminosity for gamma-rays and neutrinos (all-flavour) as a function of the energy. The values of the baryonic loading and the proton spectral index have been fixed at $10$ and $1.8$, respectively.
• Figure 2: Test statistic contour plot in terms of baryonic loading ($\eta$) and the proton spectral index ($\alpha_p$) for the joint KM3NeT/ARCA and IceCube analysis. The best-fit value is reported with a red star.
• Figure 3: Neutrino diffuse spectral energy distribution for blazars in terms of the energy for a single neutrino flavour. The dark blue solid line represents the best fit, while the shaded region is the $1\sigma$ band. The prediction is compared with the KM3-230213A equivalent flux KM3NeT:2025npi, the joint $E^{-2}$ flux obtained by KM3NeT:2025ccp including IceCube-Extreme High-Energy IceCube:2018fhm and Auger non-observations, and the updated IceCube IceCube:2025ezc and Auger differential upper limits AbdulHalim:2023SN. For comparison, the diffuse neutrino flux measured by the IceCube Neutrino Observatory with several samples IceCube:2020wumAbbasi:2021qfzIceCube:2021rpz and also the ANTARES upper limits ANTARES:2024ihw are reported. The pink and purple shaded regions represent the IceCube single-power-law (SPL) fits for High-Energy Starting Events (HESE) IceCube:2020wum and Northern Sky Tracks (NST) Abbasi:2021qfz, respectively.
• Figure 4: Gamma-ray diffuse spectral energy distribution for blazars as a function of the energy. The solid line represents the best fit while the shaded region the $1\sigma$ band. The result is compared with ExtraGalactic Background measurements of Fermi-LAT and the 2FGL sources Fermi-LAT:2014ryh.
• Figure 5: Test statistic contour plot in terms of baryonic loading ($\eta$) and the proton spectral index ($\alpha_p$) for the KM3NeT/ARCA-only analysis. The best-fit value is reported with a red star.