Time Dependence in Relativistic Collisionless Shocks: Theory of the Variable “Wisps” in the Crab Nebula
Time Dependence in Relativistic Collisionless Shocks: Theory of the Variable “Wisps” in the Crab Nebula
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相对论无碰撞激波中的时间依赖性：蟹状星云中变量“缕缕”的理论
DOI：
10.1086/381568
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
J. Arons
中科院分区：
文献类型：
--
作者：
A. Spitkovsky;J. Arons
我们描述的结果与时间相关的数值模拟的碰撞反向冲击终止脉冲星风在蟹状星云。我们把上游的相对论风的离子和电子-正电子等离子体嵌入在一个环形磁场，径向向外流动的脉冲星在一个部门周围的旋转赤道。电子-正电子对中领先激波下游离子回旋轨道的相对论回旋不稳定性发射向外传播的磁声波。由于新鲜的离子供应穿过冲击，这个时间依赖的过程实现了极限环，其中波以离子拉莫尔时间的数量级的周期性发射。在磁场和对密度与这些波，以及它们的传播速度，半定量地再现的行为，在最近的观测中获得的哈勃太空望远镜和钱德拉X射线天文台所描述的环和环的功能。通过选择离子轨道的参数来拟合小束的空间分离，我们预测了与数据一致的小束的时间变化周期。当与非热加速的机制相结合时，磁场中的压缩和与光学结构相关的等离子体密度自然地解释了蟹状星云中X射线特征的位置。本文还讨论了脉冲星风赤道电流片中高能离子的起源和加速问题。
We describe results from time-dependent numerical modeling of the collisionless reverse shock terminating the pulsar wind in the Crab Nebula. We treat the upstream relativistic wind as composed of ions and electron-positron plasma embedded in a toroidal magnetic field, flowing radially outward from the pulsar in a sector around the rotational equator. The relativistic cyclotron instability of the ion gyrational orbit downstream of the leading shock in the electron-positron pairs launches outward-propagating magnetosonic waves. Because of the fresh supply of ions crossing the shock, this time-dependent process achieves a limit cycle, in which the waves are launched with periodicity on the order of the ion Larmor time. Compressions in the magnetic field and pair density associated with these waves, as well as their propagation speed, semiquantitatively reproduce the behavior of the wisp and ring features described in recent observations obtained using the Hubble Space Telescope and the Chandra X-Ray Observatory. By selecting the parameters of the ion orbits to fit the spatial separation of the wisps, we predict the period of time variability of the wisps that is consistent with the data. When coupled with a mechanism for nonthermal acceleration of the pairs, the compressions in the magnetic field and plasma density associated with the optical wisp structure naturally account for the location of X-ray features in the Crab. We also discuss the origin of the high-energy ions and their acceleration in the equatorial current sheet of the pulsar wind.