First-principles Demonstration of Diffusive-advective Particle Acceleration in Kinetic Simulations of Relativistic Plasma Turbulence
First-principles Demonstration of Diffusive-advective Particle Acceleration in Kinetic Simulations of Relativistic Plasma Turbulence
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DOI：
10.3847/2041-8213/ab8122
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发表时间：
2019-01
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影响因子：
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通讯作者：
K. Wong;V. Zhdankin;D. Uzdensky;G. Werner;M. Begelman
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文献类型：
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作者：
K. Wong;V. Zhdankin;D. Uzdensky;G. Werner;M. Begelman
非热相对论等离子体普遍存在于脉冲星风星云和活动星系核等天体物理系统中，从它们的发射光谱可以推断。传统上，粒子加速（NTPA）的非热过程是用动量空间中的Fokker-Planck（FP）扩散-平流方程来模拟的。在这封信中，我们直接测试的FP框架在从头算动力学模拟驱动磁化湍流在相对论对等离子体。通过统计分析跟踪粒子的运动，我们证明了NTPA的扩散性质，并测量FP能量扩散（D）和平流（A）系数作为粒子能量的函数。我们发现，在高能量的非热尾，符合二阶费米加速理论的规模，但在较低的能量有一个弱得多的标度。我们还发现，A是不可忽略的，并减少NTPA倾向于拉粒子的粒子能量分布的峰值。这项研究为湍流NTPA的FP图像提供了强有力的支持，从而增强了我们对空间和天体物理等离子体的理解。
Nonthermal relativistic plasmas are ubiquitous in astrophysical systems like pulsar wind nebulae and active galactic nuclei, as inferred from their emission spectra. The underlying nonthermal particle acceleration (NTPA) processes have traditionally been modeled with a Fokker–Planck (FP) diffusion-advection equation in momentum space. In this Letter, we directly test the FP framework in ab initio kinetic simulations of driven magnetized turbulence in relativistic pair plasma. By statistically analyzing the motion of tracked particles, we demonstrate the diffusive nature of NTPA and measure the FP energy diffusion (D) and advection (A) coefficients as functions of particle energy . We find that scales as in the high-energy nonthermal tail, in line with second-order Fermi acceleration theory, but has a much weaker scaling at lower energies. We also find that A is not negligible and reduces NTPA by tending to pull particles toward the peak of the particle energy distribution. This study provides strong support for the FP picture of turbulent NTPA, thereby enhancing our understanding of space and astrophysical plasmas.