Effects of Multiscale Plasma Waves on Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks
Effects of Multiscale Plasma Waves on Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks
复制标题
弱准垂直簇内激波下多尺度等离子体波对电子预加速的影响
DOI：
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Hyesung Kang
中科院分区：
文献类型：
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作者：
J. Ha;Sunjung Kim;D. Ryu;Hyesung Kang
与合并星系团有关的射电遗迹表明，在星系团内介质中低音速马赫数(M S，≲3)的合并驱动激波中，相对论电子的加速。最近的研究表明，电子注入到扩散激波加速可以通过β=P GAS/P B≈2 0-10 0激波激波脚下的类费米加速和β≈1-5激波激波相变过程中的随机激波漂移加速发生。在这里，我们探索SSDA如何通过在足够大的二维域中执行粒子在单元中的模拟来促进在β≈20-100等离子体中的弱准垂直(Q SSD)冲击中的电子预加速度。我们发现，在ms≳MAIC*∼2.3的超临界激波中，激波斜坡下游的离子和电子温度各向异性激发了多尺度波，通过诱导波的随机螺距角散射，电子在激波跃迁中被限制了较长的时间。通过沿运动电场的梯度漂移获得能量，电子可以在这样的ICM冲击下一直被预加速到注入DSA。我们的发现表明，ICM弱激波下的电子DSA过程可以解释射电遗迹的起源。然而，由于从射电或X射线观测得到的一些观测到的射电遗迹激波的马赫数低至M S∼1.5，因此有必要用M S和Lt；2.3进一步研究亚临界激波中的电子加速。
Radio relics associated with merging galaxy clusters indicate the acceleration of relativistic electrons in merger-driven shocks with low sonic Mach numbers (M s ≲ 3) in the intracluster medium (ICM). Recent studies have suggested that electron injection to diffusive shock acceleration (DSA) could take place through the so-called Fermi-like acceleration in the shock foot of β = P gas/P B ≈ 20–100 shocks and the stochastic shock drift acceleration (SSDA) in the shock transition of β ≈ 1–5 shocks. Here, we explore how the SSDA can facilitate electron preacceleration in weak quasi-perpendicular (Q ⊥) shocks in β ≈ 20–100 plasmas by performing particle-in-cell simulations in a two-dimensional domain large enough to properly encompass ion-scale waves. We find that in supercritical shocks with Ms≳MAIC*∼2.3 , multiscale waves are excited by the ion and electron temperature anisotropies in the downstream of the shock ramp, and that through stochastic pitch-angle scattering off the induced waves, electrons are confined in the shock transition for an extended period. Gaining energy through the gradient-drift along the motional electric field, electrons could be preaccelerated all the way to injection to DSA at such ICM shocks. Our findings imply that the electron DSA process at weak ICM shocks could explain the origin of radio relics. However, a further investigation of electron acceleration at subcritical shocks with M s < 2.3 is called for, since the Mach numbers of some observed radio relic shocks derived from radio or X-ray observations are as low as M s ∼ 1.5.