Theory of Stochastic Shock Drift Acceleration for Electrons in the Shock Transition Region
Theory of Stochastic Shock Drift Acceleration for Electrons in the Shock Transition Region
复制标题
激波转变区电子随机激波漂移加速理论
DOI：
10.3847/1538-4357/ab0d8a
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
T. Amano
中科院分区：
文献类型：
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作者：
T. Katou;T. Amano
我们提出了一种新的电子加速机制，我们称之为随机冲击漂移加速（SSDA），扩展了标准的冲击漂移加速低能电子在准垂直冲击，包括随机俯仰角散射的影响。我们证明了在强散射的极限下，激波过渡区内加速电子的稳态能谱成为幂律。光谱指数与俯仰角散射系数无关。另一方面，通过该机制可获得的最大能量与俯仰角散射系数成线性比例。这些结果已被证实的Monte Carlo模拟，包括有限的俯仰角各向异性。我们发现，该理论可以合理地解释准垂直地球的弓形激波的原位观测。理论标度律表明，最大能量的增加与冲击波速度的平方成比例，这表明在准垂直超新星遗迹冲击波中，热电子可能被SSDA加速到温和的相对论能量。因此，该机制为长期存在的电子注入问题提供了一个合理的解决方案。
We propose a novel electron acceleration mechanism, which we call stochastic shock drift acceleration (SSDA), that extends the standard shock drift acceleration for low-energy electrons at a quasi-perpendicular shock to include the effect of stochastic pitch-angle scattering. We demonstrate that the steady-state energy spectrum of electrons accelerated within the shock transition region becomes a power law in the limit of strong scattering. The spectral index is independent of the pitch-angle scattering coefficient. On the other hand, the maximum energy attainable through the mechanism scales linearly with the pitch-angle scattering coefficient. These results have been confirmed by Monte Carlo simulations that include finite pitch-angle anisotropy. We find that the theory can reasonably well explain in situ observations of quasi-perpendicular Earth’s bow shock. The theoretical scaling law suggests that the maximum energy increases in proportion to the square of the shock speed, indicating that the thermal electrons may be accelerated up to mildly relativistic energies by the SSDA at quasi-perpendicular supernova remnant shocks. Therefore, the mechanism provides a plausible solution to the long-standing electron injection problem.