Can KM3-230213A be compatible with a cosmogenic origin?

TL;DR

The paper investigates whether the KM3-230213A event could be cosmogenic in origin by developing a cosmogenic neutrino framework that couples UHECR injection across five nuclear species with a proton-boosting component, a Z-dependent cutoff $E^{Z}_{\mathrm{max}}=Z E_{\mathrm{max}}$, and cosmological source evolution $S(z) \propto (1+z)^m$ up to $z_{\max}$ (examined for $z_{\max}=1$ and $6$). It computes the resulting neutrino fluxes and ARCA21 expectations using $n_{\rm exp}^{\rm ARCA21}= T^{\rm ARCA21} \sum_i \int_{\Delta\Omega_i} \int_{\Delta E} A_{\rm eff}^{\rm ARCA21}(E,\Omega) \times \Phi_{\rm model}(E,\Omega) \ dE \, d\Omega$, and analyzes how fluxes depend on $m$, $z_{\max}$, and composition. The results show that $z_{\max}=1$ yields fluxes below current sensitivity, while $z_{\max}=6$ or a subdominant proton component can raise the flux to levels compatible with KM3-230213A, thereby constraining UHECR accelerators and their evolution. Overall, the work highlights the potential of high-energy cosmogenic neutrinos to probe distant accelerators and the proton content of UHECRs in the $10^{17}$–$10^{18}$ eV range.

Abstract

On the 13th February 2023 the KM3NeT/ARCA telescope observed a track-like event compatible with a ultra-high-energy muon with an estimated energy of 120 PeV, produced by a neutrino with an even higher energy, making it the most energetic neutrino event ever detected. The reported equivalent flux suggest the possible existence of a new diffuse component. A diffuse cosmogenic flux is expected to originate from the interactions of ultra-high-energy cosmic rays with ambient photon and matter fields. Here we show that this component can be compatible with the reported flux level only integrating the cosmogenic emission, at least up to redshift ~$z = 6 $ and assuming a subdominant fraction of protons in the ultra-high-energy cosmic-ray flux, thus placing constraints on known cosmic accelerators. These conditions impose constraints on known cosmic accelerators and open a window into an unexplored region of the Universe at this energy scale.

Figures (3)

• Figure 1: Expected neutrino fluxes as a function of energy for different source evolution parameters ($m$; color-coded) at two maximum redshift values: $z_{\rm max} = 1$ (top panel) and $z_{\rm max} = 6$ (bottom panel). The blue cross indicates the flux required to produce one expected event within the central 90% CL energy range of the KM3-230213A event (horizontal span); vertical bars denote the 1$\sigma$, 2$\sigma$, and 3$\sigma$ Feldman-Cousins confidence intervals KM3NeT2024. The purple- and pink-shaded bands represent 68% confidence level contours of IceCube's single power-law fits (Northern-Sky Tracks and High-Energy Starting Events, respectively). Darker regions indicate the 90% central energy range at the best fit (dashed lines), while lighter shades are extrapolations to higher energies. Purple and pink crosses represent the respective IceCube best fits; the orange cross corresponds to the Glashow resonance event. Dotted lines show upper limits from ANTARES (95% CL), Pierre Auger, and IceCube.
• Figure 2: Expected number of events in ARCA21 as a function of source evolution $m$ for $z_{\rm max} = 1$ (circles) and $z_{\rm max} = 6$ (squares). The color scale represents the corresponding cosmic-ray emissivity required to match the UHECR spectrum at $z = 0$, as defined in Equation \ref{['emissivity']}.
• Figure 3: Expected neutrino fluxes as a function of energy assuming a secondary proton component subdominant at the highest energies. The format follows that of figure \ref{['fig:candidate']}.