Gamma-ray and Neutrino Signals from Accretion Disk Coronae of Active Galactic Nuclei

TL;DR

This paper reviews how active galactic nuclei coronae can produce gamma-ray and neutrino signals, highlighting recent observational evidence and proposing tests across multiple wavelengths and neutrino detections.

Contribution

It synthesizes current observational data and theoretical models to explore non-thermal processes in AGN coronae and suggests methods to test these models with future observations.

Findings

Recent millimeter-wave observations support non-thermal activity in AGN coronae.

IceCube detected a neutrino excess from NGC 1068, indicating high-energy particle production.

Proposed multi-messenger observational strategies to test AGN corona models.

Abstract

To explain X-ray spectra of active galactic nuclei (AGN), non-thermal activity in AGN coronae such as pair cascade models has been extensively discussed in the past literature. Although X-ray and gamma-ray observations in the 1990s disfavored such pair cascade models, recent millimeter-wave observations of nearby Seyferts establish the existence of weak non-thermal coronal activity. Besides, the IceCube collaboration reported NGC 1068, a nearby Seyfert, as the hottest spot in their 10-yr survey. These pieces of evidence are enough to investigate the non-thermal perspective of AGN coronae in depth again. This article summarizes our current observational understandings of AGN coronae and describes how AGN coronae generate high-energy particles. We also provide ways to test the AGN corona model with radio, X-ray, MeV gamma-ray, and high-energy neutrino observations.