A model for nonthermal particle acceleration in magnetic reconnection

The past decade has seen an outstanding development of nonthermal particle acceleration in magnetic reconnection, with clear signatures of power-law energy distributions as an expected outcome of first principle kinetic simulations. Here we propose a model for investigating nonthermal particle acceleration in reconnection in a systematic approach. We show that particle energy distributions are well determined by particle injection, acceleration, and escape processes. Using a series of ab initio kinetic simulations, we accurately evaluate the energy-dependent acceleration rate, energy diffusion, and escape rate. The resulting spectral characteristics, including the spectral index, lower and upper bound of the power-law distribution, agree well with the simulation results.