An Accretion Flare Interpretation for the Ultra-High-Energy Neutrino Event KM3-230213A

TL;DR

This work tackles the origin of the ultrahigh-energy neutrino KM3-230213A by proposing a super-Eddington accretion flare in the blazar MRC 0614-083, whose optical flare irradiates a surrounding dust torus and drives infrared dust echoes that serve as targets for $p\gamma$ photomeson interactions. Using a time-dependent multimessenger framework implemented with AM^3K, the authors connect the accretion-driven proton injection $L_p=\epsilon_p\dot M c^2$ (with $\epsilon_p=0.2$) to photomeson production and electromagnetic cascades, predicting a neutrino flux compatible with IceCube's lower-energy $E^{-2}$ extrapolation and X-ray cascades observed near the neutrino time. The model identifies $\tau_{p\gamma}\gg\tau_{pp}$, with IR photons ($\varepsilon_{\rm IR}\sim0.16$ eV) dominating $p\gamma$ interactions, and demonstrates that for a fiducial $z=0.5$ the neutrino peak occurs near $E_\nu\sim100$ PeV while still respecting $\gamma$-ray limits from Fermi-LAT. A key remaining uncertainty is the source redshift, which materially affects luminosity scales and the required accretion rate; the paper emphasizes the need for optical/UV spectroscopy to determine $z$ and robustly test this self-consistent, multi-messenger scenario.

Abstract

We study the origin of the ultra-high-energy (UHE) neutrino event KM3-230213A detected by KM3NeT, focusing on MRC 0614-083 which has been pinpointed as the closest blazar to the neutrino localization exhibiting variable multi-wavelength emission. A joint interpretation of the optical, infrared, and X-ray light curves suggests that MRC 0614-083 has undergone a super-Eddington accretion flare accompanied by efficient proton acceleration. That flare has initiated a delayed infrared echo within the surrounding dust torus, which serves as a target for photomeson ($pγ$) interactions such that a self-consistent picture emerges that complements the blazar jet scenario: the predicted UHE neutrino flux is at the level expected from joint $E^{-2}$ fit with the IceCube measurements at lower energies, the variable nature of the event alleviates the tension with IceCube limits, and the accompanying electromagnetic cascade describes the X-ray flare around the neutrino detection time. Since a key remaining uncertainty is the unknown redshift of the source, we strongly encourage optical/ultraviolet spectroscopic measurements to determine its redshift.

Figures (3)

• Figure 1: Observed multi-wavelength light curves of MRC 0614-083. Top panel: ZTF optical (r-band) observations (blue points) and the interpolated optical light curve (blue dashed curve). Middle panel: Infrared W2-band data from NEOWISE (red points) with the dust echo fit (solid red curve). The early-time and spherical components are shown as red dashed and red dash-dotted curves, respectively. Bottom panel: X-ray observations (black points), Fermi-LAT upper limits (green points) and results. The cascade X-ray and $\gamma$-ray light curves are shown as the black solid and green dashed-dotted curves, respectively, while the magenta dashed curve represents the light curve of single-flavor neutrinos with energies above 10 PeV. The vertical orange dashed line depicts the neutrino detection time $T_\nu$. Data sources are listed in the main text.
• Figure 2: Neutrino and cascade spectra at the neutrino detection time $T_{\nu}$ for the $z = 0.5$ case. The orange, red, blue, and green points represent the radio, infrared/optical/UV, X-ray, and $\gamma$-ray observations, respectively. The magenta point denotes the average neutrino flux derived from the KM3-230213A $E^{-2}$ fit, while the dark blue point shows the neutrino flux from the joint $E^{-2}$ fit. The upper limit from the 12.6-year IceCube search is shown as the black dashed curve. The solid black and red curves indicate the total cascade emission and the single-flavor neutrino flux, respectively. The gray dashed curve represents the target photon spectrum, and the black dotted curve shows the jet interpretation to the far-infrared observations and the archival ROSAT X-ray data (gray point).
• Figure 3: Impact of source redshift on model predictions, with $z$ varied from 0.5 (black curves), 1.0 (red), 1.5 (blue), to 2.0 (green). The left and middle panels show the X-ray light curve fits and spectral fits, respectively. The data points are the same as those in Fig. \ref{['fig:LC']} and Fig. \ref{['fig:spec']}. In the middle panel, solid curves represent cascade emissions, while dashed curves indicate the corresponding single-flavor neutrino fluxes. The right panel shows the cumulative single-flavor neutrino fluence up to $T_\nu$. The 90% CL sensitivity curves of neutrino current and future detectors are also included.