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arXiv 2011.09032astro-ph.HE
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超声速吸积流中Lense-Thirring进动能产生QPO吗?

Can Lense-Thirring precession produce QPOs in supersonic accretion flows?

G. Marcel, J. Neilsen

摘要:

X射线双星的时间特性仍然没有被理解,特别是在它们的X射线功率谱中存在准周期振荡(QPO)。Lense-Thirring进动的固体机制是一个用来解释最常见的QPO类型(C型)的突出模型。然而,固体进动需要一个特定的结构,尚未检查的约束性质的吸积流。在本文中,我们假设,作为固体岁差的要求,一个磁盘分为两个流动的过渡半径$r_t$:一个冷的外部流和一个热的内部流(扮演日冕的角色)。我们探索的物理结构,这两个流量使用模型独立的估计吸积参数。我们表明,为了重现所观察到的X射线光谱在发光的硬态,热流必须吸积在音速到超音速的速度,无法达到典型的粘性扭矩。由于这种极端的吸积速度(或高$α$参数),在这些状态下,盘的任何区域都不处于固体进动所需的“类波”状态。此外,我们期望通过半径$r_{\rm break}>r_t$内的Bardeen-Petterson效应,流与黑洞自旋轴对齐。因此,热的内部流不能表现出固体进动-目前在文献中描绘-在发光硬态。由于C型QPO在这些状态中普遍存在,我们得出结论,这种机制不太可能是在恒星质量的黑洞周围产生C型QPO的原因。

英文摘要:

The timing properties of X-ray binaries are still not understood, particularly the presence of quasi-periodic oscillations (QPOs) in their X-ray power spectra. The solid-body regime of Lense-Thirring precession is one prominent model invoked to explain the most common type of QPOs, Type C. However, solid-body precession requires a specific structure that has not been examined in light of constrained properties of accretion flows. We assume in this paper, as solid-body precession requires, a disk separated into two flows at a transition radius $r_t$: a cold outer flow and a hot inner flow (playing the role of the corona). We explore the physical structure of both flows using model-independent estimates of accretion parameters. We show that, in order to reproduce the observed X-ray spectra during luminous hard states, the hot flow must accrete at sonic to supersonic speeds, unreachable with typical viscous torques. As a result of this extreme accretion speed (or high $α$ parameter), no region of the disk during these states lies in the `wave-like' regime required for solid-body precession. Furthermore, we expect the flow to align with the black hole spin axis via the Bardeen-Petterson effect inside a radius $r_{\rm break}>r_t$. As a consequence, the hot inner flow cannot exhibit solid body precession -- as currently pictured in the literature -- during luminous hard states. Since Type C QPOs are prevalent in these states, we conclude that this mechanism is unlikely to be responsible for producing Type C QPOs around stellar mass black holes.

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