粘性吸积盘边界层中作为整体流体力学模的准周期振荡
Quasi-periodic oscillations as global hydrodynamic modes in the boundary layers of viscous accretion disks
摘要：
吸积中子星的准周期振荡（QPO）的观测特征强烈地表明，吸积盘最内层的振荡模可能是QPO的来源。中子星周围的吸积盘的内部区域可以隐藏与径向周转频率$κ$相关的非常高的频率模式。具有轨道频率$Ω$的$κ$的简并在盘和致密物体之间的磁层顶附近的非开普勒边界或过渡区中被去除。通过分析粘性吸积盘边界层中长波的整体流体动力学模，我们发现增长最快的模频率与$κ$和$κ\pm Ω$附近的频带有关.在轨道频率$Ω$最大的半径附近达到最大增长率。全局流体动力学参数，如表面密度分布和径向漂移速度，决定了在边界层中，在给定的特定半径处，自由振荡的模式将增长。根据在中子星源中观测到的kHz QPO之间的峰值分离，最快增长模式的两个连续带之间的差频总是与中子星的自旋频率有关。这是由旋转磁层施加在内盘边界区域的边界条件的自然结果。
英文摘要：
The observational characteristics of quasi-periodic oscillations (QPOs) from accreting neutron stars strongly indicate the oscillatory modes in the innermost regions of accretion disks as a likely source of the QPOs. The inner regions of accretion disks around neutron stars can harbor very high frequency modes related to the radial epicyclic frequency $κ$. The degeneracy of $κ$ with the orbital frequency $Ω$ is removed in a non-Keplerian boundary or transition zone near the magnetopause between the disk and the compact object. We show, by analyzing the global hydrodynamic modes of long wavelength in the boundary layers of viscous accretion disks, that the fastest growing mode frequencies are associated with frequency bands around $κ$ and $κ\pm Ω$. The maximum growth rates are achieved near the radius where the orbital frequency $Ω$ is maximum. The global hydrodynamic parameters such as the surface density profile and the radial drift velocity determine which modes of free oscillations will grow at a given particular radius in the boundary layer. In accordance with the peak separation between kHz QPOs observed in neutron-star sources, the difference frequency between two consecutive bands of the fastest growing modes is always related to the spin frequency of the neutron star. This is a natural outcome of the boundary condition imposed by the rotating magnetosphere on the boundary region of the inner disk.
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