Particle-in-Cell Simulations on Collisionless Shocks and Particle Acceleration in Black Hole Coronae

Multiple nearby Active Galactic Nuclei have been reported as sources of high-energy neutrinos detected by the IceCube observatory. The results strongly suggest efficient proton acceleration to (sub‑)PeV energies, likely within Black Hole (BH) Coronae, given the lack of γ-ray counterparts. The acceleration mechanisms remain unconfirmed due to limited understanding of coronal environments and challenges in modeling hot, relativistic plasmas. While diffusive shock acceleration (DSA) has been proposed, a self-consistent treatment incorporating detailed kinetic plasma effects has been absent. In this study, we present the particle-in-cell (PIC) method as a first-principles approach to investigate particle acceleration by collisionless shocks. Using large-scale 1D simulations, we surveyed possible shock parameters inferred from multi-wavelength observations of BH Coronae, focusing on previously underexplored effects, such as initial temperature ratios between ions and electrons and trans-relativistic shock velocities. We found that collisionless shocks can accelerate protons to the energies required for observed neutrino spectra under a wide range of plasma conditions. The simulations also provide insights into the energy partition between protons and electrons, offering crucial constraints on coronal plasma conditions verified by observational counterparts in radiation.