We analytically study the properties of the electromagnetic field in vacuum around close binary compact stars containing at least one neutron star. We show that the orbital motion of the neutron star induces high multipole modes of the electromagnetic field just before the merger. These modes are superimposed to form a spiral arm configuration and its edge is found to be a likely site for magnetic reconnection. These modes also enhance the total Poynting flux from neutron star binaries by a factor of 2--4. We also indicate that the electric field induced by the orbital motion lead to a magnetosphere around binaries and estimate its plasma density, which has a different parameter dependence than Goldreich-Julian density. With these properties, we discuss possible electromagnetic counterparts to gravitational wave events, and identify radio precursors, such as fast radio bursts, as the most promising observational targets.

中文翻译：

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致密双星电磁场和引力波电磁前兆的解析特性

我们分析研究了包含至少一颗中子星的紧密双星致密星周围真空中电磁场的特性。我们表明，中子星的轨道运动在合并之前诱发了电磁场的高多极模式。这些模式叠加形成螺旋臂配置，并且发现其边缘是磁重联的可能位置。这些模式还将中子星双星的总坡印廷通量提高了 2--4 倍。我们还指出轨道运动引起的电场导致双星周围的磁层并估计其等离子体密度，其具有与 Goldreich-Julian 密度不同的参数依赖性。有了这些特性，我们讨论了引力波事件的可能电磁对应物，