A Unified Framework for 10 TeV to EeV Diffuse Neutrino Sky and KM3-230213A

TL;DR

The paper proposes a unified framework in which SBO-like low-luminosity gamma-ray bursts (LL GRBs) produce a broadband neutrino sky from 10 TeV to EeV energies by coupling prompt internal-shock emission with external forward-shock afterglow in a wind-like circumburst medium. By fitting multi-wavelength data from two representative LL GRBs (GRB 060218 and GRB 100316D) and computing photohadronic neutrino production with the AMES code, the authors derive a two-component neutrino spectrum whose prompt and afterglow contributions correspond to distinct energy regimes. They show that the resulting diffuse flux can accommodate the observed data, with the GRB 060218-like population contributing at tens-to-hundreds TeV and the GRB 100316D-like population shaping the ultra-high-energy regime, potentially explaining the KM3NeT 220 PeV event. The framework provides concrete, testable predictions for next-generation neutrino observatories (GRAND, IceCube-Gen2, RNO-G) and emphasizes the role of circumburst environments and LL GRB diversity in shaping the high-energy neutrino sky, offering a physical link across energies and transient populations.

Abstract

Establishing a unified origin that simultaneously accounts for the wide-band diffuse flux and recent ultra-high-energy (UHE) detections is a pressing challenge in multi-messenger astrophysics. Successive shock regimes in shock-breakout candidates, most notably low-luminosity gamma-ray bursts (LL GRBs), naturally introduce distinct physical environments producing a multi-component neutrino flux extending from 10 TeV to the UHE regime. Integrating prompt and afterglow phases within a unified dynamical framework yields a self-consistent explanation for this broadband emission. In this work, we discuss this framework, building on MWL observations. We show that the prompt emission from GRB~060218-like events accounts for $\gtrsim 10\%$ of the diffuse flux at 100~TeV, while GRB~100316D-like configurations predict a distinct flux peak near $10^{-9}\rm~GeV~cm^{-2}~s^{-1}~sr^{-1}$ at 100~PeV, providing a physical interpretation for the 220 PeV KM3-230213A event. This decoupling explains the lack of low-energy counterparts for individual UHE detections while maintaining consistency with the total diffuse neutrino flux. Ultimately, this framework identifies SBO-like LL~GRBs as a unifying origin for these phenomena, providing a physical link across a wide band from 10 TeV to EeV energies testable by next-generation observatories, including GRAND, IceCube-Gen2, and RNO-G.

Figures (5)

• Figure 1: Multi-wavelength afterglow lightcurves for GRB 060218 (top) and GRB 100316D (bottom). Solid lines represent the posterior median of the FS model prediction, with 1$\sigma$ uncertainties (shaded), compared against observations (crosses) with 1$\sigma$ error bars or 95% C.L. upper limits (triangles). The Fermi-LAT upper limit is evaluated at 1 GeV.
• Figure 2: Predicted diffuse neutrino flux (solid lines) with 1$\sigma$ uncertainties (shaded regions) from the SBO-like LL GRB population compared to observed astrophysical neutrino fluxes (crosses) IceCube:2024fxoIceCube:2025tgpKM3NeT:2025ccp. Scenarios assume a population composed of either GRB 060218-like (blue) or GRB 100316D-like (pink) sources. The prompt (dashed) and afterglow (dotted-dashed) sub-components are shown separately, highlighting the distinct contributions to the characteristic two-hump spectral distribution.
• Figure 3: Predicted gamma ray flux representing the post-burn-in posterior parameter space for a hypothetical SBO-like LL GRB. The solid purple curve highlights the maximum predicted flux compared against the observed 95% confidence level upper limits from Fermi-LAT. The colored curves represent the parameter points along the 95% contour boundary, with colors and markers matching those in Fig. \ref{['fig:prompt_contour']}.
• Figure 4: Left: Confidence contours of the joint spectral fitting parameters for the prompt phase. Crossing points indicate the medians of the post-burn-in MCMC samples, while dashed lines mark the 1$\sigma$ HPD interval of the marginalized 1D posterior distribution. Best-fit values are provided in Table \ref{['tab:prompt_bfp']}. Right: 95% posterior region in the isotropic gamma-ray luminosity ($L_{\gamma,\rm{iso}}$) and redshift ($z$) parameter space for a hypothetical LL GRB with a GRB 100316D configuration. Stars represent parameter points at the boundary used to illustrate the predicted flux in Fig. \ref{['fig:km3_fit']}. Solid lines indicate the posterior median, while the 68% HPD boundaries are shown as dashed lines.
• Figure 5: Confidence contours of the spectral fitting parameters for GRB 060218 (left) and GRB 100316D (right). Solid lines indicate the medians of the post-burn-in MCMC samples, while dashed lines mark the 1$\sigma$ HPD interval of the marginalized 1D posterior distribution. Best fit values are provided in Table \ref{['tab:afterglow_bfp']}.