Seyfert Galaxies as Neutrino Sources: An Outflow$-$Cloud Interaction Perspective

TL;DR

This paper investigates how outflow-cloud interactions in Seyfert galaxies can produce high-energy neutrinos, potentially explaining a significant part of the diffuse astrophysical neutrino background.

Contribution

It introduces a detailed outflow-cloud interaction model for neutrino production in Seyfert nuclei, aligning with observed neutrino fluxes and explaining their contribution to the diffuse background.

Findings

The model reproduces observed TeV neutrino fluxes in five Seyfert galaxies.

Seyfert galaxies can account for a substantial fraction of the diffuse neutrino background.

The process involves AGN winds colliding with gas clouds, accelerating cosmic-ray protons.

Abstract

Following the identification of the first confirmed individual neutrino source, Seyfert galaxies have emerged as the most prominent class of high-energy neutrino emitters. In this work, we perform a detailed investigation of the outflow--cloud interaction scenario for neutrino production in Seyfert nuclei. In this framework, fast AGN-driven winds collide with clumpy gas clouds in the nuclear region, forming bow shocks that efficiently accelerate cosmic-ray protons. The accelerated protons subsequently interact with cold protons from the outflows via inelastic proton--proton ($pp$) collisions, producing high-energy neutrinos, while the photomeson ($p\gamma$) process with disk photons may provide a subdominant contribution at the highest energies. Applying this model to five neutrino-associated Seyfert galaxies, we successfully reproduce the observed TeV neutrino fluxes without violating existing gamma-ray constraints. By integrating over the Seyfert population using X-ray luminosity functions, we further demonstrate that Seyfert galaxies can account for a substantial fraction of the diffuse astrophysical neutrino background in the $10^4-10^5~{\rm GeV}$ energy range.