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 emission. Using fully kinetic particle-in-cell (PIC) simulations, we study particle injection and nonthermal particle acceleration during relativistic magnetic reconnection in an electron-positron plasma. While several different mechanisms contribute to particle injection, the mechanism primarily responsible for the high-energy power-law spectrum is a Fermi mechanism. We evaluate quantities relating to the injection and power-law acceleration over a range of guide field strengths and spatial domains. In the weak guide field regime, particle injection is dominated by mechanisms related to the electric field perpendicular to the magnetic field (Wperp), and their importance increases for larger domains. A strong guide field limits the role of Wperp, but Wperp is nevertheless increasingly important for larger domains. We also find that the power-law index p increases with the guide field strength and domain size of the simulation. These findings will help us understand the nonthermal acceleration and emissions in high-energy astrophysics, including black hole jets and pulsar wind nebulae.