Turbulent AGN coronae as the origin of diffuse neutrinos up to PeV energies

Abstract

It has been shown that the turbulence acceleration in AGN coronae can account for 1-10 TeV neutrinos from some AGNs, such as the Seyfert galaxy NGC 1068. Based on this, there are attempts to explain the diffuse neutrinos observed by IceCube with the accumulated contribution from a population of AGNs, but it is found that the maximum neutrino energy is less than tens of TeV and, as a result, additional source classes are needed to explain the high-energy component above this energy. Recently, motivated by the detection of >100 TeV neutrinos from the Seyfert galaxy NGC 7469, it was shown that the turbulence acceleration in the corona can explain >100 TeV neutrinos given a larger magnetization parameter ($σ\sim 1$) in the corona, which leads to a larger maximum proton energy and a hard proton spectrum. In this paper, we extend this assumption to the population of AGNs and study whether the population of AGNs with a wide range of magnetization can explain the entire diffuse neutrinos. We find that AGN coronae could account for the diffuse neutrinos up to PeV energies if a significant fraction of AGNs have magnetization as large as $σ\sim 1-10$. This conclusion is insensitive to the shape of the magnetization parameter distribution as long as the range of the magnetization parameter is sufficiently wide and the distribution is flat towards high magnetization. Interestingly, this model can also explain the peak of the diffuse neutrino spectrum at 30 TeV.

Figures (4)

• Figure 1: Color map of the maximum energy of protons as a function of X-ray luminosity ($L_X$) and magnetization ($\sigma$). The left dark region represents the parameter space that protons can not be efficiently accelerated (i.e. $t_{\rm tur} \gtrsim t_{\rm loss}$ and the energy loss is dominated by $pp$ and/or in-fall). The bright region at the bottom-right corner represents the maximum proton energy constrained by the Hillas condition.
• Figure 2: Diffuse all-flavor neutrino fluxes from the AGN coronae assuming that the magnetization distribution follows the log-normal distribution with parameters $\mu = -1$ and $s = 1$. The colored dashed curves denote the contributions from AGNs in the different ranges of the X-ray luminosity, while the black solid curve represents the sum of them. The blue and black data points represent IceCube observations, while the orange and blue shaded regions show the broken power-law fit reported by IceCube IceCube2025arXiv250722233A. In the calculations, we adopt $\mathcal{R} = 10$, $\eta_p \simeq 0.1$, $\eta_X \simeq 0.1$, and $\zeta \simeq 0.1$.
• Figure 3: Diffuse all-flavor neutrino fluxes from the AGN population assuming power-law distributions for the magnetization with different power-law indices, as shown in colored dot-dashed curves. For comparison, we also plot the neutrino fluxes from the AGN coronae assuming that the magnetization distribution follows the log-normal distribution, as shown by the solid black curve. The others keep the same with Fig.\ref{['Fig:Diffuse1']}.
• Figure 4: Same as the Fig.\ref{['Fig:Diffuse1']} but characterizing the contribution of each magnetization range. The colored dashed curves denote the contributions from AGNs in the different ranges of the magnetization $\sigma$, while the black solid curve represents the sum of them.