Particle acceleration and pitch-angle anisotropy resulting from magnetic reconnection are investigated in highly magnetized ion-electron plasmas. By means of fully kinetic particle-in-cell simulations, we demonstrate that magnetic reconnection generates anisotropic particle distributions fs∣cosα∣,ε , characterized by broken power laws in the particle energy spectrum f _s (ε) ∝ ε ^−p and pitch angle 〈sin2α〉∝εm . The characteristics of these distributions are determined by the relative strengths of the magnetic field’s guide and reconnecting components (B _g /B ₀) and the plasma magnetization (σ ₀). Below the injection break energy ε ₀, ion and electron energy spectra are extremely hard (p _< ≲ 1) for any B _g /B ₀ and σ ₀ ≳ 1, while above ε ₀ the spectral index steepens (p _> ≳ 2), displaying high sensitivity to both B _g /B ₀ and σ ₀. The pitch angle displays power-law ranges with negative slopes (m _<) below and positive slopes (m _>) above εminα , steepening with increasing B _g /B ₀ and σ ₀. The ratio B _g /B ₀ regulates the redistribution of magnetic energy between ions (ΔE _i ) and electrons (ΔE _e ), with ΔE _i ≫ ΔE _e for B _g /B ₀ ≪ 1, ΔE _i ∼ ΔE _e for B _g /B ₀ ∼ 1, and ΔE _i ≪ ΔE _e for B _g /B ₀ ≫ 1, with ΔE _i /ΔE _e approaching unity when σ ₀ ≫ 1. The anisotropic distribution of accelerated particles results in an optically thin synchrotron power spectrum F _ν (ν) ∝ ν ^{(2−2p+m)/(4+m)} and a linear polarization degree Π_lin = (p + 1)/(p + 7/3 + m/3) for a uniform magnetic field. Pitch-angle anisotropy also induces temperature anisotropy and eases synchrotron cooling, along with producing beamed radiation aligned with the magnetic field, which is potentially responsible for rapid frequency-dependent variability.

中文翻译：

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磁重联驱动的并行粒子加速和俯仰角各向异性：离子电子等离子体


在高度磁化的离子电子等离子体中研究了磁重联引起的粒子加速和俯仰角各向异性。通过全动态粒子胞内模拟，我们证明磁重联会产生各向异性粒子分布 fs∣cosα∣,ε ，其特征是粒子能谱 f _s (ε) ∝ ε ^-p和俯仰角中的幂律被破坏〈sin2α〉∝εm 。这些分布的特征由磁场引导和重连分量(B _g /B ₀ )以及等离子体磁化强度(σ ₀ )的相对强度决定。低于注入断裂能 ε ₀时，对于任何 B _g /B ₀和 σ ₀ ≳ 1，离子和电子能谱都极其困难 (p _< ≲ 1)，而高于 ε ₀时，谱指数变得陡峭 (p _> ≳ 2) )，对 B _g /B ₀和 σ ₀均表现出高灵敏度。桨距角显示幂律范围，εminα 下方为负斜率 (m _< )，上方为正斜率 (m _> )，随着 B _g /B ₀和 σ ₀的增加而变陡。 比率 B _g /B ₀调节离子 (ΔE) 和电子 (ΔE _e ) 之间磁能的重新分配，其中 ΔE ≫ ΔE _e对于 B _g /B ₀ ≪ 1，ΔE ∼ ΔE _e对于 B _g /B ₀ ∼ 1，对于 B _g /B ₀ ≫ 1，ΔE ≪ ΔE _e，​​当 σ ₀ ≫ 1 时，ΔE/ΔE _e接近 1。加速粒子的各向异性分布导致光学上薄的同步加速器功率谱 F _ν (ν) ∝ ν对于均匀磁场^{，(2−2p+m)/(4+m)}和线性极化度 Π _lin = (p + 1)/(p + 7/3 + m/3)。俯仰角各向异性还会引起温度各向异性并简化同步加速器冷却，同时产生与磁场对齐的束状辐射，这可能是导致频率相关快速变化的原因。