Light Echoes in Kerr Geometry: A Source of High-Frequency QPOs from Random X-Ray Bursts
Light Echoes in Kerr Geometry: A Source of High-Frequency QPOs from Random X-Ray Bursts
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克尔几何中的光回波：随机 X 射线爆发的高频 QPO 来源
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发表时间：
2007
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影响因子：
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通讯作者：
D. Kazanas
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作者：
K. Fukumura;D. Kazanas
我们提出高频准周期振荡（HFQPOs）可以由快速旋转黑洞内部等离子体随机形成的x射线爆发（闪光）产生。我们通过对其轨道的直接计算表明，构成观测到的x射线光曲线的光子，如果是由于大量这样的闪光，则会受到黑洞拖动惯性系的显著影响；每次这样的爆发的光子都以多重（双重或三重）的形式到达观测者那里，这些光子被一个大致恒定的时滞Δ flag /M≃14分开。我们认为，每一个这样的“束”代表光子沿着轨道，在光子圆轨道半径的黑洞周围有一个额外的轨道（光子“回声”）。系统响应函数中恒定滞后的存在导致其功率密度谱具有QPO特征，即使相应的光曲线由完全随机信号组成。这种效应大体上是由黑洞自旋引起的，并随着自旋参数a的减小或爆发的径向位置移出静态极限表面（遍层）而逐渐减弱。我们的计算表明，对于克尔参数为a/M = 0.99，质量为M = 10 M☉的黑洞，QPO的频率预计为νQPO ~ 1.3-1.4 kHz。我们讨论了我们的模型结果的合理性和观测意义，以及它的局限性。
We propose that high-frequency quasi-periodic oscillations (HFQPOs) can be produced from randomly formed X-ray bursts (flashes) by plasma interior to the ergosphere of a rapidly rotating black hole. We show by direct computation of their orbits that the photons comprising the observed X-ray light curves, if due to a multitude of such flashes, are significantly affected by the black hole’s dragging of inertial frames; the photons of each such burst arrive to an observer at infinity in multiple (double or triple), distinct “bunches” separated by a roughly constant time lag of Δ tlag/M ≃ 14, regardless of the bursts’ azimuthal position. We argue that every other such “bunch” represents photons that follow trajectories with an additional orbit around the black hole at the photon circular orbit radius (a photon “echo”). The presence of this constant lag in the response function of the system leads to a QPO feature in its power density spectra, even though the corresponding light curve consists of a totally stochastic signal. This effect is by and large due to the black hole spin and is shown to gradually diminish as the spin parameter a decreases or the radial position of the burst moves outside the static limit surface (ergosphere). Our calculations indicate that for a black hole with Kerr parameter of a/M = 0.99 and mass of M = 10 M☉, the QPO is expected at a frequency of νQPO ∼ 1.3–1.4 kHz. We discuss the plausibility and observational implications of our model results, as well as its limitations.