Neutrino and Cascade Gamma-Ray Emission from Magnetized Turbulent Coronae in Seyfert Galaxies

TL;DR

This paper investigates whether magnetized, turbulent coronae in Seyfert galaxies can simultaneously produce high-energy neutrinos and cascading gamma rays via hadronic interactions of non-resonantly accelerated protons. Using a disk-corona model and a Fokker-Planck treatment of proton transport, the authors relate the neutrino output to the X-ray luminosity and trace the role of gamma-ray absorption and subsequent electromagnetic cascades that yield MeV emission. The results predict a visible MeV cascade component with luminosity comparable to the neutrino flux and a non-linear L_nu-L_gamma relation that depends on the coronal size, notably favoring compact coronae. These predictions provide a concrete multi-messenger framework to test the hadronic corona scenario with future MeV telescopes (AMEGO-X, e-ASTROGAM) and neutrino observatories. The work thus links X-ray coronal physics to IceCube-like neutrino signals and enables targeted, multi-messenger searches for Seyfert sources.

Abstract

Recent neutrino observations from the IceCube Collaboration suggest that Seyfert galaxies are promising candidate sources of neutrinos. Within the standard disk-corona model, we assume that protons are accelerated by a non-resonant acceleration mechanism driven by magnetized turbulence in the corona. These accelerated protons interact with ambient radiation or matter, producing high-energy neutrinos and gamma rays. In this scenario, gamma rays are largely absorbed within the corona. The neutrino luminosity depends primarily on the properties of the corona (such as the X-ray luminosity and radius) and the spectral energy distribution of the target photons. This study demonstrates the relation between the neutrino luminosity and the X-ray luminosity, and further discusses the contribution of cascade gamma rays to coronal radiation. Notably, MeV gamma rays can effectively escape the source, together with neutrinos, and serve as key observational probes for testing this model. Future MeV gamma-ray telescopes, such as AMEGO-X and e-ASTROGAM, are expected to detect such gamma-ray signatures, providing a critical multi-messenger test of the hadronic corona model.

Figures (6)

• Figure 1: Spectral energy distributions of the target photon field under different X-ray luminosities correspond to the calculation results with parameter $\mathcal{R}=10$. Curves for different X-ray luminosity values are labeled in the legend.
• Figure 2: Spectral energy distributions of non-thermal protons under different X-ray luminosities correspond to the calculation results with parameter $\mathcal{R}=10$. Curves for different X-ray luminosity values are labeled in the legend.
• Figure 3: Timescales for different processes considered in this study, at $\mathcal{R}=10$ for different X-ray luminosity values of $L_{X}=10^{42}~{\rm erg}~{\rm s}^{-1}$ (left), $10^{43}~{\rm erg}~{\rm s}^{-1}$ (middle), and $10^{44}~{\rm erg}~{\rm s}^{-1}$ (right).
• Figure 4: The gamma-ray and neutrino spectra emanating from NGC 1068 are presented here. The black solid lines denote the $95$% contour lines and the best-fit curve derived from IceCube data IceCube:2022der, while the green and orange points represent gamma-ray observations from Fermi-LAT Ajello:2023hkh and MAGIC MAGIC:2019fvw, respectively. The purple and black solid lines represent the sensitivities of AMEGO-X Caputo:2022xpx and e-ASTROGAM e-ASTROGAM:2016bph for observation times of 0.6 years and 1 year, respectively. The black dash-dotted line illustrates the tail of X-ray emission originating from the corona. The all-flavor neutrino spectrum (depicted as a red solid line) and the cascade photon spectrum (shown as a blue solid line) are the computational outcomes corresponding to parameters $L_{X} = 7 \times 10^{43}~{\rm erg}~{\rm s}^{-1}$ and $\mathcal{R} = 10$.
• Figure 5: (Left) Spectral energy distributions of neutrinos (red) and cascade photons (blue) under different X-ray luminosities correspond to the calculation results with parameter $\mathcal{R}=10$. Curves for different X-ray luminosity values are labeled in the legend. (Right) The neutrino luminosity above 300 GeV is shown as a function of the gamma-ray luminosity $L_{\gamma,~{0.1 - 1000}~{\rm MeV}}$, comprising contributions from both coronal and cascade photons.