Particle Acceleration in Mildly Relativistic Shearing Flows: The Interplay of Systematic and Stochastic Effects, and the Origin of the Extended High-energy Emission in AGN Jets
Particle Acceleration in Mildly Relativistic Shearing Flows: The Interplay of Systematic and Stochastic Effects, and the Origin of the Extended High-energy Emission in AGN Jets
复制标题
DOI：
10.3847/1538-4357/aa7410
复制
发表时间：
2017-06
期刊：
影响因子：
--
通讯作者：
Ruo-Yu Liu;F. Rieger;F. Aharonian
中科院分区：
文献类型：
--
作者：
Ruo-Yu Liu;F. Rieger;F. Aharonian
活动星系核（AGN）大尺度喷流中扩展X射线辐射的起源对传统的加速和辐射模型提出了挑战。虽然电子同步辐射被认为是最可行的辐射机制，但连续大尺度X射线结构的形成仍然是一个悬而未决的问题。由于天体物理喷流预计会表现出一些湍流和剪切运动，因此我们在这里研究剪切流促进颗粒延长加速的潜力，并评估其对所得颗粒分布的影响。我们的治疗结合了系统剪切和随机二阶费米效应。我们发现，对于适用于大规模活动星系核喷流的典型参数，随机二阶费米加速，它总是伴随着剪切粒子加速，可以发挥重要的作用，在促进整个过程中的粒子粒子加速。我们研究了随时间变化的粒子分布的存在下，二阶费米加速，剪切加速，和同步辐射损失，使用一个简单的福克-普朗克方法，并提供插图可能出现的复杂的（多组分）粒子能量分布与不同的光谱分支。我们提出了适用于大规模活动星系核喷流的典型参数的例子，表明了理解扩展X射线发射和超高能宇宙射线起源的基本过程的相关性。
The origin of the extended X-ray emission in the large-scale jets of active galactic nuclei (AGNs) poses challenges to conventional models of acceleration and emission. Although electron synchrotron radiation is considered the most feasible radiation mechanism, the formation of the continuous large-scale X-ray structure remains an open issue. As astrophysical jets are expected to exhibit some turbulence and shearing motion, we here investigate the potential of shearing flows to facilitate an extended acceleration of particles and evaluate its impact on the resultant particle distribution. Our treatment incorporates systematic shear and stochastic second-order Fermi effects. We show that for typical parameters applicable to large-scale AGN jets, stochastic second-order Fermi acceleration, which always accompanies shear particle acceleration, can play an important role in facilitating the whole process of particle energization. We study the time-dependent evolution of the resultant particle distribution in the presence of second-order Fermi acceleration, shear acceleration, and synchrotron losses using a simple Fokker–Planck approach and provide illustrations for the possible emergence of a complex (multicomponent) particle energy distribution with different spectral branches. We present examples for typical parameters applicable to large-scale AGN jets, indicating the relevance of the underlying processes for understanding the extended X-ray emission and the origin of ultrahigh-energy cosmic rays.