Baryon loading of active galactic nucleus jets mediated by neutrons

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 the 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 ~ 2 × 10^-3. Mc² and mass loading Mj ~ 6 × 10^-4 M for the case of the BH mass M ~ 10⁸ M, where M is the mass accretion rate. The terminal Lorentz factors of the jets are Γ ~ 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., Γ ~ 50 for L _j,tot ~ 3 × 10^-2 Mc².