湍流磁场中辐射超相对论电子的动量扩散
On the Momentum Diffusion of Radiating Ultrarelativistic Electrons in a Turbulent Magnetic Field
摘要：
在这里，我们调查的超相对论性电子的随机加速磁湍流的一些方面。特别是，我们讨论了由于与湍流MHD模式的共振相互作用而发生动量扩散的粒子的稳态能谱，严格考虑了与不同辐射冷却过程相关的直接能量损失。对于磁湍流，我们假设一个给定的功率谱的类型$W(k) \propto k^{-q}$。然而，与以前的方法相比，我们假设一个有限范围的湍流波矢量$k$，考虑各种湍流谱指数$1 =< q =< 2$，并集中在一个非常低效的粒子逃逸的情况下，从加速网站。我们发现，对于不同的冷却和注入条件，随机加速过程往往建立一个修改后的超相对论麦克斯韦分布的辐射粒子，与高能量指数截止形状的冷却和加速率之间的相互作用。例如，如果主导辐射过程的时间尺度与电子动量成比例为$\propto p^r$，则所得到的电子能量分布具有$n_e(p) \propto p^2 exp[ - (1 / a) (p / p_eq)^a]$的形式，其中$a = 2-q-r$和$p_eq$是由随机加速和能量损失时间尺度之间的平衡定义的平衡动量。我们还讨论了更详细的同步辐射和逆康普顿发射光谱所产生的这样的电子能量分布，考虑到克莱因西科效应。我们指出，这些光谱的高频率段的曲率，即使是由相同的人口的电子，可能是实质上不同的同步加速器和逆康普顿组件之间。
英文摘要：
Here we investigate some aspects of stochastic acceleration of ultrarelativistic electrons by magnetic turbulence. In particular, we discuss the steady-state energy spectra of particles undergoing momentum diffusion due to resonant interactions with turbulent MHD modes, taking rigorously into account direct energy losses connected with different radiative cooling processes. For the magnetic turbulence we assume a given power spectrum of the type $W(k) \propto k^{-q}$. In contrast to the previous approaches, however, we assume a finite range of turbulent wavevectors $k$, consider a variety of turbulence spectral indexes $1 =< q =< 2$, and concentrate on the case of a very inefficient particle escape from the acceleration site. We find that for different cooling and injection conditions, stochastic acceleration processes tend to establish a modified ultrarelativistic Maxwellian distribution of radiating particles, with the high-energy exponential cut-off shaped by the interplay between cooling and acceleration rates. For example, if the timescale for the dominant radiative process scales with the electron momentum as $\propto p^r$, the resulting electron energy distribution is of the form $n_e(p) \propto p^2 exp[ - (1 / a) (p / p_eq)^a]$, where $a = 2-q-r$, and $p_eq$ is the equilibrium momentum defined by the balance between stochastic acceleration and energy losses timescales. We also discuss in more detail the synchrotron and inverse-Compton emission spectra produced by such an electron energy distribution, taking into account Klein-Nishina effects. We point out that the curvature of the high frequency segments of these spectra, even though being produced by the same population of electrons, may be substantially different between the synchrotron and inverse-Compton components.
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