标题： X射线变异性在黑洞候选体中的相位滞后和相干性 显示英文标题

标题： Phase Lags and Coherence of X-Ray Variability in Black Hole Candidates

摘要： 黑洞候选体的“低”（硬或“非热”）状态有时通过一个光学厚、高温的康普顿云来建模，该云遮蔽了一个较软的输入源，例如吸积盘。 在这些模型中，观测到的输出光谱完全由云重新处理的光子组成，这使得难以提取关于输入光谱的信息。 最近，Miller（1995）提出，实际中硬X射线和软X射线光子之间的傅里叶相位（或时间）滞后代表了输入源本身的相位滞后，只是乘以一个因子。 因此，相位滞后将成为输入光子源的探测手段。 在本文中，我们检验了这一说法，并发现尽管对于Miller所考虑的有限参数空间是正确的，但一旦输出光子能量远大于输入光子能量，固有相位滞后就会消失。 剩余的时间滞后是由于云中平均扩散时间差异产生的“平台”。 如Miller指出的那样，这个平台的幅度——即使在固有时间滞后仍然存在时——表明了康普顿云的大小和温度，并且是两个比较能量的函数。 然而，我们发现使用之前的仪器如Ginga，如果存在平台，很可能被计数噪声所掩盖。 从相干函数中可能获得更灵敏的康普顿云参数测量，该函数是从傅里叶交叉功率谱密度的幅度导出的。 该函数在天鹅座X-1中已被观察到在高频傅里叶频率下呈指数下降。 相干性的损失是康普顿云在时间尺度长于约10秒的情况下发生大小和/或温度大幅变化的特征。 我们认为，观察相位滞后和相干性 显示英文摘要

摘要： The ``low'' (hard or ``non-thermal'') state of black hole candidates is sometimes modelled via an optically thick, hot Compton cloud that obscures a softer input source such as an accretion disk. In these models the observed output spectra consist entirely of photons reprocessed by the cloud, making it difficult to extract information about the input spectra. Recently Miller (1995) has argued that the Fourier phase (or time) lag between hard and soft X-ray photons in actuality represents the phase lags intrinsic to the input source, modulo a multiplicative factor. The phase lags thus would be a probe of the input photon source. In this paper we examine this claim and find that, although true for the limited parameter space considered by Miller, the intrinsic phase lag disappears whenever the output photon energy is much greater than the input photon energy. The remaining time lags represent a ``shelf'' due to differences between mean diffusion times across the cloud. As pointed out by Miller, the amplitude of this shelf -- which is present even when the intrinsic time lags remain -- is indicative of the size and temperature of the Compton cloud and is a function of the two energies being compared. However, we find that with previous instruments such as Ginga the shelf, if present, was likely obscured by counting noise. A more sensitive measure of Compton cloud parameters may be obtainable from the coherence function, which is derived from the amplitude of the Fourier cross power spectral density. This function has been seen to exponentially decrease at high Fourier frequencies in Cygnus X-1. Coherence loss is characteristic of Compton clouds that undergo large variations of size and/or temperature on time scales longer than about 10 seconds. We argue that observing phase lags and coherence