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arXiv 1104.1091astro-ph.HEgr-qc
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合并和坍缩致密物体的电磁功率

Electromagnetic power of merging and collapsing compact objects

Maxim Lyutikov

摘要:

[摘要]电磁辐射可以作为合并的前兆产生,作为NS坍缩期间和所产生的BH自旋下降阶段的即时发射。我们证明了轴对称无力磁场的时间演化可以用双曲型Grad-Shafranov方程来表示。在史瓦西几何中,我们发现了由自旋和坍缩NS驱动的磁层的精确的非线性含时劈裂结构。基于这个解决方案,我们认为,崩溃的NS到BH顺利发生,没有自然形成的电流片或其他耗散结构的开放场线,因此,不允许磁场成为断开连接的明星和逃逸到无穷大。因此,只要一个孤立的克尔黑洞能够产生等离子体和电流,它就不会失去它的开放磁场线,它的磁层结构朝着分裂的方向发展,黑洞就会电磁地自旋下来。假设外部介质是真空的“无毛定理”在这种情况下不适用:高导电等离子体引入了禁止磁场线与BH断开的拓扑约束。最终,一个随机的大规模自发重联事件将导致磁场释放,永远关闭电磁BH引擎。我们还讨论了短的伽马射线暴的性质,并建议,早期余辉性质的相似性的长和短的伽玛暴可以有关的事实,即在这两种情况下,一个旋转BH可以保留足够长的时间,以提取其旋转能量的大部分,并通过风中的内部耗散产生高能量的发射磁场。

英文摘要:

[Abridged] Electromagnetic emission can be produced as a precursor to the merger, as a prompt emission during the collapse of a NS and at the spin-down stage of the resulting BH. We demonstrate that the time evolution of the axisymmetric force-free magnetic fields can be expressed in terms of the hyperbolic Grad-Shafranov equation. We find exact non-linear time-dependent split-monopole structure of magnetosphere driven by spinning and collapsing NS in Schwarzschild geometry. Based on this solution, we argue that the collapse of a NS into the BH happens smoothly, without natural formation of current sheets or other dissipative structures on the open field lines and, thus, does not allow the magnetic field to become disconnected from the star and escape to infinity. Thus, as long as an isolated Kerr BH can produce plasma and currents, it does not lose its open magnetic field lines, its magnetospheric structure evolved towards a split monopole and the BH spins down electromagnetically. The "no hair theorem", which assumes that the outside medium is a vacuum, is not applicable in this case: highly conducting plasma introduces a topological constraint forbidding the disconnection of the magnetic field lines from the BH. Eventually, a single random large scale spontaneous reconnection event will lead to magnetic field release, shutting down the electromagnetic BH engine forever. We also discuss the nature of short Gamma Ray Bursts and suggest that the similarity of the early afterglows properties of long and short GRBs can be related to the fact that in both cases a spinning BH can retains magnetic field for sufficiently long time to extract a large fraction of its rotation energy and produce high energy emission via the internal dissipation in the wind.

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