Electron Firehose Instabilities in High-β Intracluster Shocks
Electron Firehose Instabilities in High-β Intracluster Shocks
复制标题
高β团内激波中的电子消防不稳定性
DOI：
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发表时间：
2019
影响因子：
4.9
通讯作者：
Hyesung Kang
中科院分区：
文献类型：
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作者：
Sunjung Kim;J. Ha;D. Ryu;Hyesung Kang
通过反射和激波漂移加速(SDA)的电子预加速度对于非热电子在无碰撞激波中的扩散激波加速是必不可少的。前人的研究表明，在星系团内介质中弱准垂直(Q⊥)激波中，由于β反射电子引起的温度各向异性可以驱动电子的火管不稳定性，从而激发激波脚中的非传播斜波。本文通过线性分析和粒子模拟，研究了β∼-100ICM等离子体中由电子温度各向异性和漂移电子束驱动的火管不稳定性。EBFI应该更适合于描述Q⊥激波中上游波的自激发，因为激波脚中的回流电子表现得更像电子束，而不是各向异性的双麦克斯韦粒子。我们发现这两个不稳定性的基本性质，如生长速率、γ和快速增长的斜模的波数，在ICM环境中是相似的，但有一个例外：当ETAFI激发的波是非传播的(ωr=0)时，由EBFI激发的波有一个非零频率()。然而，ωr<；γ的频率较小。因此，我们得出的结论是，基于ETAFI的前人对上游波性质的解释仍然适用于ICM中的Q⊥-Shock。
The preacceleration of electrons through reflection and shock drift acceleration (SDA) is essential for the diffusive shock acceleration of nonthermal electrons in collisionless shocks. Previous studies suggested that, in weak quasi-perpendicular (Q⊥) shocks in the high-β ( ) intracluster medium (ICM), the temperature anisotropy due to SDA-reflected electrons can drive the electron firehose instability, which excites oblique nonpropagating waves in the shock foot. In this paper, we investigate, through a linear analysis and particle-in-cell simulations, the firehose instabilities driven by an electron temperature anisotropy (ETAFI) and also by a drifting electron beam (EBFI) in β ∼ 100 ICM plasmas. The EBFI should be more relevant to describing the self-excitation of upstream waves in Q⊥-shocks, since backstreaming electrons in the shock foot behave more like an electron beam rather than an anisotropic bi-Maxwellian population. We find that the basic properties of the two instabilities, such as the growth rate, γ, and the wavenumber of fast-growing oblique modes, are similar in the ICM environment, with one exception; while the waves excited by the ETAFI are nonpropagating (ωr = 0), those excited by the EBFI have a nonzero frequency ( ). However, the frequency is small with ωr < γ. Thus, we conclude that the interpretation of previous studies for the nature of upstream waves based on the ETAFI remains valid in Q⊥-shocks in the ICM.