Can magnetic reconnection power neutrino emission from AGN coronae?

TL;DR

This study explores whether magnetic reconnection in SMBH coronae can accelerate protons to produce high-energy neutrinos, with a case study of NGC 1068, showing consistency with observed neutrino and X-ray data.

Contribution

It demonstrates that reconnection-driven acceleration in SMBH coronae can produce the nonthermal protons needed for neutrino emission, aligning with observations of NGC 1068.

Findings

Protons can be accelerated up to tens of PeV before cooling limits apply.

The predicted TeV neutrino spectrum matches NGC 1068 observations without fitting the spectral slope.

Coronal parameters are constrained by IceCube and X-ray luminosities, indicating transrelativistic magnetization.

Abstract

We investigate whether reconnection of small-scale current sheets in transrelativistic supermassive black hole (SMBH) coronae can supply the nonthermal protons needed for high-energy neutrino emission, using NGC 1068 as a test case. We model the corona as a strongly turbulent, low-$\beta$, collisionless hydrogen plasma with characteristic size $r_{\rm co}$, magnetic field strength $B$, proton density $n_p$, and radiation energy density $u_{\rm rad}$. Combining the observed IceCube-band neutrino luminosity with the X-ray luminosity and Thomson optical depth reduces these coronal quantities to a one-parameter family. Across this family, the proton magnetization $\sigma_p \equiv B^2/(4\pi n_p m_p c^2)$ is transrelativistic with $\sigma_p \sim 0.3$. In this regime, we show that repeated encounters with intermittent reconnecting current sheets can energize suprathermal protons up to tens of PeV before photomeson cooling limits further acceleration. These injected particles may then be further processed by stochastic interactions with the turbulent cascade. Motivated by PIC simulations of strong turbulence at comparable magnetization, we adopt a nonthermal proton spectrum with an independently specified index and find that the predicted TeV spectral shape is broadly consistent with NGC~1068 without fitting the proton spectral slope.