Particle Injection and Nonthermal Particle Acceleration in Relativistic Magnetic Reconnection

Magnetic reconnection in the relativistic regime has been proposed as an important process for efficiently accelerating particles and producing high-energy emissions. Using fully kinetic PIC simulations, we investigate how guide field strength and domain size affect two stages of particle energization: (1) acceleration from the upstream thermal energy to the injection energy and (2) the further acceleration responsible for high-energy power-law spectra. In the first stage, we evaluate the contributions of parallel electric fields, Fermi reflections, and pickup acceleration. For weak guide fields, Fermi reflections and pickup acceleration dominate both stages. For a strong guide field, however, parallel electric fields decisively dominate particle injection but contribute comparably to perpendicular electric fields to total acceleration. We also find that the power-law index and injection energy increase with guide field strength and converge with increasing domain size. These findings will help explain the nonthermal acceleration and emissions in black hole jets and pulsar wind nebulae.