TeV neutrinos and hard X-rays from relativistic reconnection in the corona of NGC 1068

TL;DR

This paper proposes that magnetic reconnection in the corona of NGC 1068 accelerates protons, producing neutrinos and X-rays consistent with recent observations, by modeling the proton spectrum and energy interactions.

Contribution

It introduces a model where relativistic magnetic reconnection accelerates protons in NGC 1068's corona, explaining neutrino and X-ray emissions with a specific proton spectrum and energy transfer mechanisms.

Findings

Protons are accelerated with a broken power-law spectrum in the corona.

Neutrino flux matches IceCube observations with a spectral index of about 3.

Gamma-ray cascades produce a moderate Compton-thick corona.

Abstract

The recent discovery of astrophysical neutrinos from the Seyfert galaxy NGC 1068 suggests the presence of non-thermal protons within a compact "coronal" region close to the central black hole. The acceleration mechanism of these non-thermal protons remains elusive. We show that a large-scale magnetic reconnection layer, of the order of a few gravitational radii, may provide such a mechanism. In such a scenario, rough energy equipartition between magnetic fields, X-ray photons, and non-thermal protons is established in the reconnection region. Motivated by recent three-dimensional particle-in-cell simulations of relativistic reconnection, we assume that the spectrum of accelerated protons is a broken power law, with the break energy being constrained by energy conservation (i.e., the energy density of accelerated protons is at most comparable to the magnetic energy density). The proton spectrum is $dn_p/dE_p\propto E_p^{-1}$ below the break, and $dn_p/dE_p\propto E_p^{-s}$ above the break, with IceCube neutrino observations suggesting $s \simeq 3$. Protons above the break lose most of their energy within the reconnection layer via photohadronic collisions with the coronal X-rays, producing a neutrino signal in good agreement with the recent observations. Gamma-rays injected in photohadronic collisions are cascaded to lower energies, sustaining the population of electron-positron pairs that makes the corona moderately Compton thick.