Efficient Production of High-Energy Nonthermal Particles During Magnetic Reconnection in a Magnetically Dominated Ion–electron Plasma

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 /(4πn(m i + m e )c 2 ), the magnetization for each species is σ i ∼ σ 0 and σ e ∼ (m i /m e )σ 0 , respectively. We have studied the magnetically dominated regime by varying σ e = 10 3 − 10 5 with initial ion and electron temperatures T i = T e = 5 − 20m 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 be ∼ σ e and γ bi ∼ 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.

Particle acceleration during magnetic reconnection in a low-beta pair plasma

“…In the simulations with magnetically-dominated proton-electron plasmas, both electrons and protons develop significant power-law distributions [49]. On the other hand, Sironi & Spitkovsky [16] argued that the initial nonthermal energization at the X-line regions is crucial for the generation of the power-law distribution [63,65].…”

“…While earlier numerical studies have identified multiple acceleration processes [9,[11][12][13][14]17], recent simulations have revealed an efficient nonthermal acceleration that gives hard powerlaw like energy distributions [16,18,19,[46][47][48][49]. In this paper, we summarize the relevant progress in this area.…”

Radiation and Polarization Signatures of the 3d Multizone Time-Dependent Hadronic Blazar Model

“…which represents a rapid particle acceleration mechanism, such as diffusive shock acceleration and magnetic reconnection (Guo et al 2016) on time scales much shorter than the time resolution of our simulation. In addition to this process, the emission region may contain microscopic turbulence, which will mediate stochastic second-order Fermi acceleration.…”

“…Guo et al (2016) have performed comprehensive PIC simulations to show that both electrons and protons can be effectively accelerated during magnetic reconnection events. As the detailed simulation of a reconnection event is beyond the scope of this paper, we simply assume that the particle injection is enhanced and the magnetic field is weakened in the disturbance, and keep the particle injection index the same as in the quiescent state.…”

Force-free collisionless current sheet models with non-uniform temperature and density profiles

“…In this section, we present some illustrative plots of the DF (24) to show the effect of changing c, i.e., the effect of changing the energy dependence of the different particle populations. In the v x -and v y -directions, it is possible to choose sets of parameters for which there are multiple peaks in the DF, which may have implications for the stability of the equilibrium.…”