Baryon Loading of AGN Jets Mediated by Neutrons

TL;DR

This paper investigates how relativistic neutrons produced in AGN accretion flows can escape and decay into protons, contributing to jet formation and mass loading, especially in low-luminosity AGN jets.

Contribution

It introduces a model for neutron-mediated baryon loading in AGN jets, quantifying efficiencies and jet properties based on neutron decay from accretion flows.

Findings

Neutron decay can deposit significant energy and mass into AGN jets.

Jet Lorentz factors can reach up to ~50 with neutron decay as a dominant mass loader.

The process explains low-luminosity AGN jets and complements other energy input mechanisms.

Abstract

Plasmas of geometrically thick, black hole (BH) accretion flows in active galactic nuclei (AGNs) are generally collisionless for protons, and involve magnetic field turbulence. Under such conditions a fraction of protons can be accelerated stochastically and create relativistic neutrons via nuclear collisions. These neutrons can freely escape from the accretion flow and decay into protons in dilute polar region above the rotating BH to form relativistic jets. We calculate geometric efficiencies of the neutron energy and mass injections into the polar region, and show that this process can deposit luminosity as high as L_j ~ 2e-3 dot{M} c^2 and mass loading dot{M}_j ~ 6e-4 dot{M} for the case of the BH mass M ~ 1e8 M_sun, where dot{M} is mass accretion rate. The terminal Lorentz factors of the jets are Gamma ~ 3, and they may explain the AGN jets having low luminosities. For higher luminosity jets, which can be produced by additional energy inputs such as Poynting flux, the neutron decay still can be a dominant mass loading process, leading to e.g., Gamma ~ 50 for L_{j,tot} ~ 3e-2 dot{M}c^2.