Luminous accreting stellar mass and supermassive black holes produce power–law continuum X-ray emission from a compact central corona. Reverberation time lags occur due to light travel time delays between changes in the direct coronal emission and corresponding variations in its reflection from the accretion flow. Reverberation is detectable using light curves made in different X-ray energy bands, since the direct and reflected components have different spectral shapes. Larger, lower frequency, lags are also seen and are identified with propagation of fluctuations through the accretion flow and associated corona. We review the evidence for X-ray reverberation in active galactic nuclei and black hole X-ray binaries, showing how it can be best measured and how it may be modelled. The timescales and energy dependence of the high-frequency reverberation lags show that much of the signal is originating from very close to the black hole in some objects, within a few gravitational radii of the event horizon. We consider how these signals can be studied in the future to carry out X-ray reverberation mapping of the regions closest to black holes.

中文翻译：

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吸积黑洞周围的 X 射线混响

发光的吸积恒星质量和超大质量黑洞从致密的中央日冕产生幂律连续谱 X 射线辐射。由于直接日冕发射的变化与其从吸积流反射的相应变化之间的光传播时间延迟，会出现混响时滞。由于直接和反射分量具有不同的光谱形状，因此可以使用在不同 X 射线能带中制作的光变曲线来检测混响。更大、更低频率的滞后也被观察到，并被识别为通过吸积流和相关日冕的波动传播。我们回顾了活动星系核和黑洞 X 射线双星中 X 射线混响的证据，展示了如何最好地测量它以及如何对其进行建模。高频混响滞后的时间尺度和能量依赖性表明，大部分信号来自非常靠近某些物体的黑洞，在事件视界的几个引力半径内。我们考虑未来如何研究这些信号，以对最接近黑洞的区域进行 X 射线混响映射。