Neutrino and pair creation in reconnection-powered coronae of accreting black holes

TL;DR

This paper explores how relativistic protons in black hole coronae contribute to neutrino production and pair enrichment, affecting X-ray emission and potentially explaining recent IceCube neutrino observations.

Contribution

It introduces a model linking proton acceleration, neutrino emission, and pair production in AGN coronae with two key parameters, advancing understanding of coronal physics.

Findings

Proton-photon interactions produce enough pairs for significant optical depths at high Eddington ratios.

Neutrino luminosity scales with the square of X-ray luminosity over Eddington luminosity below a critical ratio.

The model applied to Seyfert galaxies offers insights into neutrino emission consistent with IceCube data.

Abstract

A ubiquitous feature of accreting black hole systems is their hard X-ray emission which is thought to be produced through Comptonization of soft photons by electrons and positrons in the vicinity of the black hole, in a region with optical depth of order unity. The origin and composition of this Comptonizing region, known as the corona, is a matter open for debate. In this paper we investigate the role of relativistic protons accelerated in black-hole magnetospheric current sheets for the pair enrichment and neutrino emission of AGN coronae. Our model has two free parameters, namely the proton plasma magnetization $\sigma_{\rm p}$, which controls the peak energy of the neutrino spectrum, and the Eddington ratio $\lambda_{\rm X, Edd}$ (defined as the ratio between X-ray luminosity $L_{\rm X}$ and Eddington luminosity $L_{\rm Edd}$), which controls the amount of energy transferred to secondary particles. For sources with $\lambda_{\rm X, Edd} \gtrsim \lambda_{\rm Edd, crit}$ (where $\lambda_{\rm Edd, crit} \sim 10^{-1}$ for $\sigma_{\rm p}=10^5$ or $\sim 10^{-2}$ for $\sigma_{\rm p}=10^7$), proton-photon interactions and $ \gamma \gamma$ annihilation produce enough secondary pairs to achieve Thomson optical depths $\tau_{\rm T} \sim 0.1-10$. In the opposite case of $\lambda_{\rm X, Edd} \lesssim \lambda_{\rm Edd, crit}$, the coronal pairs cannot originate only from hadronic interactions. Additionally, we find that the neutrino luminosity scales as $L^2_{\rm X}/L_{\rm Edd}$ for $\lambda_{\rm X, Edd} \lesssim \lambda_{\rm Edd, crit}$, while it is proportional to $L_{\rm X}$ for higher $\lambda_{\rm X, Edd}$ values. We apply our model to four Seyfert galaxies, including NGC 1068, and discuss our results in light of recent IceCube observations.