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arXiv 2107.09702astro-ph.HEastro-ph.EPphysics.plasm-ph
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耦合双星、自旋轨道共振和耀斑中的磁拓扑

Magnetic topology in coupled binaries, spin-orbital resonances, and flares

Sergey A. Cherkis, Maxim Lyutikov

摘要:

我们考虑磁耦合旋转双星的拓扑结构(例如,合并中子星或相互作用的恒星-行星系统)。我们讨论的条件时,恒星的自旋和轨道运动几乎“补偿”对方,导致非常{ \it慢}整体绕组的耦合磁场;缓慢绕组配置允许逐渐积累的磁能,这是最终释放的耀斑时,达到不稳定的阈值。我们发现,这种缓慢的缠绕可以是全球性的和/或本地的。我们描述的拓扑结构的相关空间$\mathbb{F}=T^1S^2$的单位切丛的两个球,并找到条件缓慢的绕组配置的磁矩,自旋和轨道动量。这些条件在拓扑分叉点附近变得模糊不清;在某些情况下,它们还取决于自旋和轨道运动的相对相位。在合并磁化中子星的情况下,如果其中一颗恒星是毫秒脉冲星,以$\sim$ 10毫秒的速度旋转,那么在合并前大约1秒,就会发生全局共振$ω_1+ω_2= 2 Ω$(自旋加拍频是轨道周期的两倍);耀斑的总能量可以与总磁能的$10\%$一样大,产生亮度的爆发$\sim 10^{44}$ erg s $^{-1}$。高阶局部共振可以具有类似的功率,因为所涉及的磁通量管的量可以与总连接通量相当。

英文摘要:

We consider topological configurations of the magnetically coupled spinning stellar binaries (e.g., merging neutron stars or interacting star-planet systems). We discuss conditions when the stellar spins and the orbital motion nearly `compensate' each other, leading to very {\it slow} overall winding of the coupled magnetic fields; slowly winding configurations allow gradual accumulation of magnetic energy, that is eventually released in a flare when the instability threshold is reached. We find that this slow winding can be global and/or local. We describe the topology of the relevant space $\mathbb{F}=T^1S^2$ as the unit tangent bundle of the two-sphere and find conditions for slowly winding configurations in terms of magnetic moments, spins and orbital momentum. These conditions become ambiguous near the topological bifurcation points; in certain cases they also depend on the relative phases of the spin and orbital motions. In the case of merging magnetized neutron stars, if one of the stars is a millisecond pulsar, spinning at $\sim$ 10 msec, the global resonance $ω_1+ω_2= 2 Ω$ (spin-plus beat is two times the orbital period) occurs approximately a second before the merger; the total energy of the flare can be as large as $10\%$ of the total magnetic energy, producing bursts of luminosity $\sim 10^{44}$ erg s$^{-1}$. Higher order local resonances may have similar powers, since the amount of involved magnetic flux tubes may be comparable to the total connected flux.

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