SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. I. ACCELERATION EFFICIENCY
SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. I. ACCELERATION EFFICIENCY
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DOI：
10.1088/0004-637x/783/2/91
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发表时间：
2014-03-10
影响因子：
4.9
通讯作者：
Spitkovsky, A.
中科院分区：
文献类型：
--
作者：
Caprioli, D.;Spitkovsky, A.
我们使用二维和三维混合（动力学离子-流体电子）模拟来研究非相对论天体物理冲击下的粒子加速和磁场放大。我们表明，扩散激波加速度适用于准平行配置（即，当背景磁场几乎与激波法线对齐时），并且对于大音速和阿尔芬尼马赫数，产生通用幂律谱α p(-4)，其中p是粒子动量。加速离子的最大能量随时间的增加而增加，它只受有限的盒子尺寸和运行时间的限制。加速度主要对平行和准平行强激波有效，其中10%-20%的体动能可转化为高能粒子，而对准垂直激波无效。此外，磁湍流的产生与有效离子加速有关，并且在准垂直构型中消失。在非常斜的激波下，离子可以通过激波漂移加速来加速，但它们只获得几个动量因子，并且它们的最大能量不随时间增加。这些发现与观测到的极化程度以及射电和x射线同步辐射的形态一致，例如在SN 1006的残骸中。我们还讨论了离子谱（超热区）中从热粒子到非热粒子的转变，并确定了有效粒子加速特有的两个动力学特征，即上游前体的形成和标准激波跳跃条件的改变。
We use two-dimensional and three-dimensional hybrid (kinetic ions-fluid electrons) simulations to investigate particle acceleration and magnetic field amplification at non-relativistic astrophysical shocks. We show that diffusive shock acceleration operates for quasi-parallel configurations (i.e., when the background magnetic field is almost aligned with the shock normal) and, for large sonic and Alfvenic Mach numbers, produces universal power-law spectra alpha p(-4) , where p is the particle momentum. The maximum energy of accelerated ions increases with time, and it is only limited by finite box size and run time. Acceleration is mainly efficient for parallel and quasi-parallel strong shocks, where 10%-20% of the bulk kinetic energy can be converted to energetic particles and becomes ineffective for quasi-perpendicular shocks. Also, the generation of magnetic turbulence correlates with efficient ion acceleration and vanishes for quasi-perpendicular configurations. At very oblique shocks, ions can be accelerated via shock drift acceleration, but they only gain a factor of a few in momentum and their maximum energy does not increase with time. These findings are consistent with the degree of polarization and the morphology of the radio and X-ray synchrotron emission observed, for instance, in the remnant of SN 1006. We also discuss the transition from thermal to non-thermal particles in the ion spectrum (supra-thermal region) and we identify two dynamical signatures peculiar of efficient particle acceleration, namely, the formation of an upstream precursor and the alteration of standard shock jump conditions.