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

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 $\ddot{I}{ƒ}_{\mathrm{p}}$, which controls the peak energy of the neutrino spectrum, and the Eddington ratio $\hat{I}{»}_{\mathrm{X},\mathrm{Edd}}$ (defined as the ratio between X-ray luminosity $L_{\mathrm{X}}$ and Eddington luminosity $L_{\mathrm{Edd}}$), which controls the amount of energy transferred to secondary particles. For sources with $\hat{I}{»}_{\mathrm{X},\mathrm{Edd}}\gtrsim \hat{I}{»}_{\mathrm{Edd},\mathrm{crit}}$ (where $\hat{I}{»}_{\mathrm{Edd},\mathrm{crit}}\sim 10^{-1}$ for $\ddot{I}{ƒ}_{\mathrm{p}}=10^5$ or $\sim 10^{-2}$ for $\ddot{I}{ƒ}_{\mathrm{p}}=10^7$), proton-photon interactions and ${\hat{I}}^3{\hat{I}}^3$ annihilation produce enough secondary pairs to achieve Thomson optical depths $\ddot{I}{„}_{\mathrm{T}}\sim 0.1-10$. In the opposite case of $\hat{I}{»}_{\mathrm{X},\mathrm{Edd}}\lesssim \hat{I}{»}_{\mathrm{Edd},\mathrm{crit}}$, the coronal pairs cannot originate only from hadronic interactions. Additionally, we find that the neutrino luminosity scales as $L_{\mathrm{X}}^2/L_{\mathrm{Edd}}$ for $\hat{I}{»}_{\mathrm{X},\mathrm{Edd}}\lesssim \hat{I}{»}_{\mathrm{Edd},\mathrm{crit}}$, while it is proportional to $L_{\mathrm{X}}$ for higher $\hat{I}{»}_{\mathrm{X},\mathrm{Edd}}$ values. We apply our model to four Seyfert galaxies, including NGC 1068, and discuss our results in light of recent IceCube observations.

33 pages, Published on JCAP (JCAP04(2025)075)

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• Reconnection-driven Flares in M87*: Proton-Synchrotron-powered GeV Emission
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• Neutrinos from extreme astrophysical sources