Multi-messenger tests of cosmic-ray acceleration in radiatively inefficient accretion flows

TL;DR

This paper models high-energy emissions from radiatively inefficient accretion flows in low-luminosity AGNs to assess their detectability with future multi-messenger observatories, aiming to understand their role in cosmic-ray acceleration.

Contribution

It provides a detailed model of RIAFs in LLAGNs and predicts multi-messenger signals, evaluating their detectability with upcoming experiments.

Findings

Future experiments like e-ASTROGAM and IceCube-Gen2 can detect MeV gamma rays and neutrinos from LLAGNs.

Detection of high-energy gamma rays from electromagnetic cascades remains challenging.

LLAGNs could significantly contribute to the diffuse gamma-ray and neutrino backgrounds.

Abstract

The cores of active galactic nuclei (AGNs) have been suggested as the sources of IceCube neutrinos, and recent numerical simulations have indicated that hot AGN coronae of Seyfert galaxies and radiatively inefficient accretion flows (RIAFs) of low-luminosity AGNs (LLAGNs) may be promising sites of ion acceleration. We present detailed studies on detection prospects of high-energy multi-messenger emissions from RIAFs in nearby LLAGNs. We construct a model of RIAFs that can reproduce the observational features of the current X-ray observations of nearby LLAGNs. We then calculate the high-energy particle emissions from nearby individual LLAGNs, including MeV gamma rays from thermal electrons, TeV--PeV neutrinos produced by non-thermal protons, and sub-GeV to sub-TeV gamma rays from proton-induced electromagnetic cascades. We find that, although these are beyond the reach of current facilities, proposed future experiments such as e-ASTROGAM and IceCube-Gen2 should be able to detect the MeV gamma rays and the neutrinos, respectively, or else they can place meaningful constraints on the parameter space of the model. On the other hand, the detection of high-energy gamma rays due to the electromagnetic cascades will be challenging with the current and near-future experiments, such as Fermi and Cherenkov Telescope Array. In an accompanying paper, we demonstrate that LLAGNs can be a source of the diffuse soft gamma-ray and TeV--PeV neutrino backgrounds, whereas in the present paper, we focus on the prospects for multi-messenger tests which can be applied to reveal the nature of the high-energy neutrinos and photons from LLAGNs.