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arXiv 1012.2770astro-ph.HE
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电流驱动不稳定性的三维相对论磁流体动力学模拟。II。脉冲星风星云的弛豫

Three-Dimensional Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability. II. Relaxation of Pulsar Wind Nebula

Yosuke Mizuno, Yuri Lyubarsky, Ken-Ichi Nishikawa, Philip E. Hardee

摘要:

作为脉冲星风星云的模型,我们研究了含有环形磁场的流体静力热等离子体柱在电流驱动扭折不稳定性作用下的弛豫。在我们的模拟中,CD扭结不稳定性是由一个小的初始速度扰动激发的,并在热等离子体柱内形成湍流结构。我们证明,如Begelman所设想的,环向应力下降,轴附近的初始气体压力过剩减少。当CD扭结不稳定性饱和时,磁化参数σ(坡印亭与动能通量的比率)从初始值0.3下降到约0.01。我们的模拟表明,轴对称模型强烈高估了脉冲星风星云的伸长。因此,可以放弃以前对极低脉冲星风磁化的要求。观测到的脉冲星风星云的结构并不与这样一个自然假设相矛盾,即在交变场消散后,磁能通量仍然占总能通量的很大一部分。

英文摘要:

We have investigated the relaxation of a hydrostatic hot plasma column containing toroidal magnetic field by the Current-Driven (CD) kink instability as a model of pulsar wind nebulae. In our simulations the CD kink instability is excited by a small initial velocity perturbation and develops turbulent structure inside the hot plasma column. We demonstrate that, as envisioned by Begelman, the hoop stress declines and the initial gas pressure excess near the axis decreases. The magnetization parameter σ, the ratio of the Poynting to the kinetic energy flux, declines from an initial value of 0.3 to about 0.01 when the CD kink instability saturates. Our simulations demonstrate that axisymmetric models strongly overestimate the elongation of the pulsar wind nebulae. Therefore, the previous requirement for an extremely low pulsar wind magnetization can be abandoned. The observed structure of the pulsar wind nebulae do not contradict the natural assumption that the magnetic energy flux still remains a good fraction of the total energy flux after dissipation of alternating fields.

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