相对论吸积盘中的准周期振荡、俘获惯性波与强环向磁场
Quasi-periodic oscillations, trapped inertial waves and strong toroidal magnetic fields in relativistic accretion discs
AI总结：
本文通过局部和全局线性分析，发现强环向磁场可减弱垂直磁场的不利影响，恢复r-modes俘获区与ISCO的隔离，表明磁场对俘获惯性模式的负面影响小于此前预期。
摘要：
黑洞吸积盘内区由扭曲和偏心率激发的俘获惯性波（r-modes）可能解释在银河系X射线双星辐射中观测到的高频准周期振荡（HFQPOs）。然而，有观点认为强垂直磁场会将振荡的俘获区推向最内稳定圆轨道（ISCO），那里的条件可能不利于其激发。本文通过局部和全局线性分析，探讨了同时具有环向和垂直分量的大尺度磁场的影响。我们发现，强环向磁场可以减弱垂直场的不利影响：事实上，接近热强度的环向磁场可以恢复俘获区与ISCO的隔离。环向场将r-modes与吸积盘的磁声学响应耦合，并增大振荡内的有效压力。因此，与垂直磁场张力相关的恢复力被减弱。鉴于穿有极向磁力线的吸积盘会发展出强环向分量的解析和数值证据，我们的结果进一步证明磁场对俘获惯性模式的不利影响并不像以前认为的那么大。
英文摘要：
The excitation of trapped inertial waves (r-modes) by warps and eccentricities in the inner regions of a black hole accretion disc may explain the high-frequency quasi-periodic oscillations (HFQPOs) observed in the emission of Galactic X-ray binaries. However, it has been suggested that strong vertical magnetic fields push the oscillations' trapping region toward the innermost stable circular orbit (ISCO), where conditions could be unfavourable for their excitation. This paper explores the effects of large-scale magnetic fields that exhibit \textit{both} toroidal and vertical components, through local and global linear analyses. We find that a strong toroidal magnetic field can reduce the detrimental effects of a vertical field: in fact, the isolation of the trapping region from the ISCO may be restored by toroidal magnetic fields approaching thermal strengths. The toroidal field couples the r-modes to the disc's magneto-acoustic response and inflates the effective pressure within the oscillations. As a consequence, the restoring force associated with the vertical magnetic field's tension is reduced. Given the analytical and numerical evidence that accretion discs threaded by poloidal magnetic field lines develop a strong toroidal component, our result provides further evidence that the detrimental effects of magnetic fields on trapped inertial modes are not as great as previously thought.
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