Efficient Production of High-energy Nonthermal Particles during Magnetic Reconnection in a Magnetically-dominated Ion-Electron Plasma

Fan Guo; Xiaocan Li; Hui Li; William Daughton; Bing Zhang; Nicole Lloyd-Ronning; Yi-Hsin Liu; Haocheng Zhang; Wei Deng

doi:10.3847/2041-8205/818/1/L9

paper

Efficient Production of High-energy Nonthermal Particles during Magnetic Reconnection in a Magnetically-dominated Ion-Electron Plasma

arXiv:1511.01434 · doi:10.3847/2041-8205/818/1/L9

Abstract

Magnetic reconnection is a leading mechanism for dissipating magnetic energy and accelerating nonthermal particles in Poynting-flux dominated flows. In this letter, we investigate nonthermal particle acceleration during magnetic reconnection in a magnetically-dominated ion-electron plasma using fully kinetic simulations. For an ion-electron plasma with the total magnetization $σ_{0} = B^{2} / (4 π n (m_{i} + m_{e}) c^{2})$ , the magnetization for each species is $σ_{i} \sim σ_{0}$ and $σ_{e} \sim (m_{i} / m_{e}) σ_{0}$ , respectively. We have studied the magnetically dominated regime by varying $σ_{e} = 1 0^{3} - 1 0^{5}$ with initial ion and electron temperatures $T_{i} = T_{e} = 5 - 20 m_{e} c^{2}$ and mass ratio $m_{i} / m_{e} = 1 - 1836$ . The results demonstrate that reconnection quickly establishes power-law energy distributions for both electrons and ions within several ( $2 - 3$ ) light-crossing times. For the cases with periodic boundary conditions, the power-law index is $1 < s < 2$ for both electrons and ions. The hard spectra limit the power-law energies for electrons and ions to be $γ_{b e} \sim σ_{e}$ and $γ_{bi} \sim σ_{i}$ , respectively. The main acceleration mechanism is a Fermi-like acceleration through the drift motions of charged particles. When comparing the spectra for electrons and ions in momentum space, the spectral indices $s_{p}$ are identical as predicted in Fermi acceleration. We also find that the bulk flow can carry a significant amount of energy during the simulations. We discuss the implication of this study in the context of Poynting-flux dominated jets and pulsar winds especially the applications for explaining the nonthermal high-energy emissions.

7 pages, 5 figures. ApJL in press

Efficient Production of High-energy Nonthermal Particles during Magnetic Reconnection in a Magnetically-dominated Ion-Electron Plasma

Abstract

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