High-energy Neutrino Emission from a Radiatively Inefficient Accretion Flow with a Three-dimensional General Relativistic Magnetohydrodynamic Simulation

Abstract The high-energy particle production in the accretion flow onto black holes can be key physics to explain the high-energy neutrino background. While the single-zone approximation has been commonly adopted in studies of the high-energy neutrino emission around black holes, the effects of the global plasma structure may be nonnegligible. We carry out the first computations of cosmic-ray acceleration and high-energy neutrino emission via the hadronuclear ( pp ) interaction in global radiatively inefficient accretion flows and outflows around a supermassive black hole, using three-dimensional general relativistic magnetohydrodynamic simulation data. The Fokker–Planck equation for cosmic-ray protons is solved with a phenomenological model for the energy diffusion coefficient to express the turbulent acceleration in the subgrid scale. The inhomogeneous and time variable structure of the accretion flow leads to a variety of particle energy distributions. The spectral energy distributions (SEDs) of neutrinos emitted from the entire region are flatter than those calculated under the single-zone approximation. In our model, the neutrino emission originating from cosmic rays advected with the outflow rather than the inflow predominates the SEDs. Such galactic nuclei can be significant sources of cosmic rays in those galaxies.