Kinetic turbulence in shining pair plasma: intermittent beaming and thermalization by radiative cooling
Kinetic turbulence in shining pair plasma: intermittent beaming and thermalization by radiative cooling
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DOI：
10.1093/mnras/staa284
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发表时间：
2019-08
影响因子：
4.8
通讯作者：
V. Zhdankin;D. Uzdensky;G. Werner;M. Begelman
中科院分区：
文献类型：
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作者：
V. Zhdankin;D. Uzdensky;G. Werner;M. Begelman
高能天体物理系统经常包含无碰撞的相对论等离子体，它们被湍流级联加热，并被辐射冷却。了解这种辐射湍流的性质是极端等离子体天体物理学的前沿。在本文中，我们使用粒子模拟研究外部逆康普顿辐射的影响，在光学薄，相对论对等离子体驱动的湍流。我们专注于统计稳态（注入能量与辐射能量平衡），并执行从低磁化到高磁化（0.04 <$σ 11）的参数扫描。我们证明了全球粒子能量分布是准热在所有的模拟，只有一个适度的人口的非热高能粒子（延长的尾巴的一个因素的100%）。这表明非热粒子加速（在类似的非辐射模拟中观察到）被强辐射冷却淬灭。准热能分布很好地拟合的分析模型，其中随机粒子加速度（由于，例如，二阶费米机制或回旋共振相互作用）是由辐射反作用力平衡。尽管等离子体的有效热化，非热高能粒子确实在全球动量分布的各向异性中作为高度可变的间歇性光束（对于高磁化情况）显着出现。束流高能粒子在空间上与间歇性电流片重合，这表明局部磁重联可能是动力学束流的一种机制。这种光束现象可以解释在各种天体物理系统中观察到的快速耀斑（如耀变体喷流，蟹状星云和人马座A*）。
High-energy astrophysical systems frequently contain collision-less relativistic plasmas that are heated by turbulent cascades and cooled by emission of radiation. Understanding the nature of this radiative turbulence is a frontier of extreme plasma astrophysics. In this paper, we use particle-in-cell simulations to study the effects of external inverse Compton radiation on turbulence driven in an optically thin, relativistic pair plasma. We focus on the statistical steady state (where injected energy is balanced by radiated energy) and perform a parameter scan spanning from low magnetization to high magnetization (0.04 ≲ σ ≲ 11). We demonstrate that the global particle energy distributions are quasi-thermal in all simulations, with only a modest population of non-thermal energetic particles (extending the tail by a factor of ∼2). This indicates that non-thermal particle acceleration (observed in similar non-radiative simulations) is quenched by strong radiative cooling. The quasi-thermal energy distributions are well fit by analytic models in which stochastic particle acceleration (due to, e.g. second-order Fermi mechanism or gyroresonant interactions) is balanced by the radiation reaction force. Despite the efficient thermalization of the plasma, non-thermal energetic particles do make a conspicuous appearance in the anisotropy of the global momentum distribution as highly variable, intermittent beams (for high magnetization cases). The beamed high-energy particles are spatially coincident with intermittent current sheets, suggesting that localized magnetic reconnection may be a mechanism for kinetic beaming. This beaming phenomenon may explain rapid flares observed in various astrophysical systems (such as blazar jets, the Crab nebula, and Sagittarius A*).