RELATIVISTIC MAGNETOSONIC SHOCK-WAVES IN SYNCHROTRON SOURCES - SHOCK STRUCTURE AND NONTHERMAL ACCELERATION OF POSITRONS
RELATIVISTIC MAGNETOSONIC SHOCK-WAVES IN SYNCHROTRON SOURCES - SHOCK STRUCTURE AND NONTHERMAL ACCELERATION OF POSITRONS
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DOI：
10.1086/171296
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发表时间：
1992-05-10
影响因子：
4.9
通讯作者：
LANGDON, AB
中科院分区：
文献类型：
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作者：
HOSHINO, M;ARONS, J;LANGDON, AB
我们研究了与同步辐射天体物理源相关的电子-正电子-重离子等离子体中的相对论性、横向、磁声无碰撞激波的理论性质。我们使用一维电磁粒子模拟和准线性理论来研究这些非线性流动的空间和动力学结构。所有的上游离子都被冲击波阵面电磁反射，导致冲击波中的磁场强度超过其最终的下游值，形成一系列长的压缩振荡，其波长与离子的Larmor半径相当，其刚度与下游流相适应。其中旋转的反射重离子以共同发射的左手磁声波的形式耗散它们的能量，所述左手磁声波被紧邻离子反射区域后面的正电子共振吸收。当重离子的上游能量超过电子和正电子的能量时，能量在γ-m（e）+ c2和（gamma + d-gamma）m（e）+ c2之间的正电子具有N（gamma）d-gamma与γ（-s）成比例的谱，其中s约为2。当上游流的洛伦兹因子为gamma-1时，下游正电子谱的幂律部分从gamma = gamma-1扩展到gamma =（m（ion）/Zm（e +/-）gamma-1。最高能量的正电子的拉莫尔半径与冲击波的厚度相当。将流动能量转化为这些高度加速的粒子的效率约为10%-约20%。我们认为，这里发现的正电子的非热加速也适用于电子的部分加速。我们还指出了另一种加速机制，这可能是重要的斜shocks.We简要概述这些结果的应用程序的脉冲星风的终止冲击和终止冲击的喷流从活动星系核。我们的动力学冲击加速模型可以解释蟹状星云中观测到的同步辐射的光谱范围，从红外到高能伽马射线，以及从河外射电源热点看到的无线电发射。我们建议，从蟹状星云的光发射中看到的“小缕”是在作为冲击的一部分形成的压缩磁过冲中形成的亮度增强，因此，在这个系统中，终止蟹状星云脉冲星相对论风的冲击的结构是空间分辨的。这个模型意味着来自脉冲星的风的能量通量主要是部分电离的铁离子，尽管成对的铁离子在数量上形成了主导物种，整体流速对应于洛伦兹因子约10（6），每个铁离子的能量对应于与脉冲星的开放场线相关的电势能的约20%。
We study the theoretical properties of relativistic, transverse, magnetosonic collisionless shock waves in electron-positron-heavy ion plasmas of relevance to astrophysical sources of synchrotron radiation. We use both one-dimensional electromagnetic particle-in-cell simulations and quasi-linear theory to examine the spatial and kinetic structure of these nonlinear flows. All the upstream ions are electromagnetically reflected from the shock front, causing the magnetic field strength in the shock to overshoot its final downstream value in a series of long compressional oscillations with wavelengths comparable to the Larmor radius of ions with the rigidity appropriate to the downstream flow.We describe a new process of shock acceleration of nonthermal positrons, in which the gyrating reflected heavy ions dissipate their energy in the form of collectively emitted, left-handed magnetosonic waves which are resonantly absorbed by the positrons immediately behind the ion reflection region. This absorption gives rise to an ultrarelativistic downstream positron spectrum The positrons with energy between gamma-m(e) + c2 and (gamma + d-gamma)m(e) + c2 have a spectrum N(gamma)d-gamma is-proportional-to gamma(-s) with s approximately 2 when the upstream flow energy of the heavy ions exceeds that of the electrons and positrons. When the Lorentz factor of the upstream flow is gamma-1, the power-law part of the downstream positron spectrum extends from gamma = gamma-1, to gamma = (m(ion)/Zm(e +/-)gamma-1. The highest energy positrons have Larmor radii comparable to the thickness of the shock. The efficiency of conversion of flow energy into these highly accelerated particles is about 10% approximately 20%. We argue that the nonthermal acceleration of positrons found here also applies to the partial acceleration of electrons. We also point out another acceleration mechanism which may be important in oblique shocks.We briefly outline applications of these results to the termination shocks of pulsar winds and to the termination shocks of jets emanating from active galactic nuclei. Our kinetic shock acceleration model can account for the spectral range of the synchrotron radiation observed in the Crab Nebula from the infrared through high-energy gamma rays, as well as for the radio emission seen from the hot spots in extragalactic radio sources. We propose that the "wisps" seen in the optical emission from the Crab Nebula are brightness enhancements formed in the compressonal magnetic overshoots formed as part of the shock, so that the structure of the shock terminating the relativistic wind from the Crab pulsar is spatially resolved in this system. This model implies the wind from the pulsar has its energy flux largely in partially ionized iron ions, although pairs form the dominant species by number, with the bulk flow velocity corresponding to Lorentz factor approximately 10(6), and an energy per iron ion corresponding to approximately 20% of the electric potential energy associated with the open field lines of the pulsar.