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arXiv 1708.06362astro-ph.HEgr-qc
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毫秒脉冲星四种吸积态的广义相对论模拟

General-Relativistic Simulations of Four States of Accretion onto Millisecond Pulsars

Kyle Parfrey, Alexander Tchekhovskoy

摘要:

吸积中子星可以为各种天体物理现象提供动力,包括短持续时间和长持续时间的伽马射线暴、超亮X射线源和X射线双星。数值模拟是研究吸积盘-磁层相互作用的一个有价值的工具,这是这些问题的核心,最明显的是最近发现的过渡毫秒双星。然而,磁流体动力学(MHD)方法,广泛用于模拟吸积,有困难的高磁化恒星磁层,而力的方法,适用于这样的地区,不能包括吸积气体。我们提出了一种MHD方法,可以稳定地发展基本上没有力,高度磁化的区域,并描述了第一个依赖于时间的相对论模拟磁化吸积到毫秒星系。我们的轴对称广义相对论MHD模拟的第一次演示了如何与脉冲星的电磁风的湍流吸积流的相互作用,可以导致一个孤立的脉冲星的吸积状态的过渡。这种转变自然会导致相对论喷流的形成,其能量可以大大超过孤立脉冲星风的能量。如果吸积率低于临界值,脉冲星就会排出吸积流。更一般地说,我们的模拟第一次产生了四种可能的吸积状态,按质量吸积率递减的顺序排列:(a)破碎磁层和直接吸积;(b)磁通道吸积到恒星两极;(c)螺旋桨状态,物质通过轻圆柱体进入,但被离心屏障阻止吸积;(d)脉冲星风几乎完全将吸积流排除在光柱之外。

英文摘要:

Accreting neutron stars can power a wide range of astrophysical phenomena including short- and long-duration gamma-ray bursts, ultra-luminous X-ray sources, and X-ray binaries. Numerical simulations are a valuable tool for studying the accretion-disk--magnetosphere interaction that is central to these problems, most clearly for the recently discovered transitional millisecond pulsars. However, magnetohydrodynamic (MHD) methods, widely used for simulating accretion, have difficulty in highly magnetized stellar magnetospheres, while force-free methods, suitable for such regions, cannot include the accreting gas. We present an MHD method that can stably evolve essentially force-free, highly magnetized regions, and describe the first time-dependent relativistic simulations of magnetized accretion onto millisecond pulsars. Our axisymmetric general-relativistic MHD simulations for the first time demonstrate how the interaction of a turbulent accretion flow with a pulsar's electromagnetic wind can lead to the transition of an isolated pulsar to the accreting state. This transition naturally leads to the formation of relativistic jets, whose power can greatly exceed the power of the isolated pulsar's wind. If the accretion rate is below a critical value, the pulsar instead expels the accretion stream. More generally, our simulations produce for the first time the four possible accretion regimes, in order of decreasing mass accretion rate: (a) crushed magnetosphere and direct accretion; (b) magnetically channeled accretion onto the stellar poles; (c) the propeller state, where material enters through the light cylinder but is prevented from accreting by the centrifugal barrier; (d) almost perfect exclusion of the accretion flow from the light cylinder by the pulsar wind.

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