强弯曲时空中轨道运动模的功率密度谱：获得可观测信号
Power density spectra of modes of orbital motion in strongly curved spacetime: obtaining the observable signal
摘要：
在几个吸积低质量双星的X射线光变中出现了高频准周期振荡（HF QPO）。在一系列的工作中，有人建议这些QPO可能与靠近吸积盘内缘的不均匀性有关。在本文中，我们探讨的外观所产生的可观测信号的小辐射圆形热点移动沿准椭圆轨道接近最内层的稳定圆轨道在史瓦西时空。我们的考虑考虑到了以罗西X射线定时探测器（RXTE）为代表的过去二十年中一直在运行的天文台的能力，以及以大型X射线定时天文台（LOFT）为代表的拟议的未来仪器。为了这些目的，我们选择这样的模型参数，导致光变曲线与银河系黑洞源，特别是微类星体GRS 1915 + 105中观察到的光变曲线。我们发现，当一个弱信号对应的热点开普勒频率是周围的RXTE可探测性的限制，LOFT观测可以清楚地揭示其第一和第二谐波。此外，在某些特定的情况下，也可以检测光斑的径向周转频率。最后，我们还比较了斑点产生的信号与轴对称周转圆盘振荡模式产生的信号，并讨论了通过拟议的未来技术可以识别的关键差异。我们的结论是，识别信号的谐波含量的能力可以帮助区分不同的物理模型。
英文摘要：
High frequency quasi-periodic oscillations (HF QPOs) appear in the X-ray variability of several accreting low-mass binaries. In a series of works it was suggested that these QPOs may have connection to inhomogeneities orbiting close to an inner edge of the accretion disc. In this paper we explore the appearance of an observable signal generated by small radiating circular hot spots moving along quasi-elliptic trajectories close to the innermost stable circular orbit in the Schwarzschild spacetime. Our consideration takes into account the capabilities of observatories that have been operating in the past two decades represented by the Rossi X-ray Timing Explorer (RXTE) and the proposed future instruments represented by the Large Observatory for X-ray Timing (LOFT). For these purposes we choose such model parameters that lead to lightcurves comparable to those observed in Galactic black hole sources, in particular the microquasar GRS 1915+105. We find that when a weak signal corresponding to the hot-spot Keplerian frequency is around the limits of the RXTE detectability, the LOFT observations can clearly reveal its first and second harmonics. Moreover, in some specific situations the radial epicyclic frequency of the spot can be detected as well. Finally, we also compare the signal produced by the spots to the signal produced by axisymmetric epicyclic disc-oscillation modes and discuss the key differences that could be identified via the proposed future technology. We conclude that the ability to recognize the harmonic content of the signal can help to distinguish between the different proposed physical models.
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