A magnetized strongly turbulent corona as the source of neutrinos from NGC 1068

TL;DR

This paper proposes that magnetized turbulence around the supermassive black hole in NGC 1068 accelerates cosmic rays rapidly, explaining the observed high-energy neutrino flux through a self-consistent model.

Contribution

It introduces a new self-consistent theory of neutrino production that accounts for non-resonant stochastic cosmic ray acceleration in magnetized turbulence, aligning with recent simulation results.

Findings

Turbulent magnetic fields exceeding 1% of rest mass energy explain neutrino flux normalization.

Rapid cosmic ray acceleration occurs due to non-resonant stochastic processes.

The model matches the observed neutrino spectral shape from NGC 1068.

Abstract

The cores of active galactic nuclei (AGN) are potential accelerators of 10-100 TeV cosmic rays, in turn producing high-energy neutrinos. This picture was confirmed by the compelling evidence of a TeV neutrino signal from the nearby active galaxy NGC 1068, leaving open the question of which is the site and mechanism of cosmic ray acceleration. One candidate is the magnetized turbulence surrounding the central supermassive black hole. Recent particle-in-cell simulations of magnetized turbulence indicate that stochastic cosmic ray acceleration is non-resonant, in contrast to the assumptions of previous studies. We show that this has important consequences on a self-consistent theory of neutrino production in the corona, leading to a more rapid cosmic ray acceleration than previously considered. The turbulent magnetic field fluctuations needed to explain the neutrino signal are consistent with a magnetically powered corona. We find that strong turbulence, with turbulent magnetic energy density higher than $1\%$ of the rest mass energy density, naturally explains the normalization of the IceCube neutrino flux, in addition to the neutrino spectral shape. Only a fraction of the protons in the corona, which can be directly inferred from the neutrino signal, are accelerated to high energies. Thus, in this framework, the neutrino signal from NGC 1068 provides a testbed for particle acceleration in magnetized turbulence.