X-ray reverberation echoes are assumed to be produced in the strongly distorted spacetime around accreting supermassive black holes. This signal allows us to spatially map the geometry of the inner accretion flow^1,2—a region that cannot yet be spatially resolved by any telescope—and provides a direct measure of the black hole mass and spin. The reverberation timescale is set by the light travel path between the direct emission from a hot X-ray corona and the reprocessed emission from the inner edge of the accretion disk^3,4,5,6. However, there is an inherent degeneracy in the reverberation signal between black hole mass, inner disk radius and height of the illuminating corona above the disk. Here we use a long X-ray observation of the highly variable active galaxy IRAS 13224−3809 to track the reverberation signal as the system evolves on timescales of a day^7,8. With the inclusion of all the relativistic effects, modelling reveals that the height of the X-ray corona increases with increasing luminosity, providing a dynamic view of the inner accretion region. This simultaneous modelling allows us to break the inherent degeneracies and obtain an independent timing-based estimate for the mass and spin of the black hole. The uncertainty on black hole mass is comparable to the leading optical reverberation method⁹, making X-ray reverberation a powerful technique, particularly for sources with low optical variability¹⁰.

X 射线混响回波被认为是在吸积的超大质量黑洞周围强烈扭曲的时空中产生的。该信号使我们能够在空间上绘制内部吸积流^1,2的几何图形——一个尚未被任何望远镜在空间上解析的区域——并提供对黑洞质量和自旋的直接测量。混响时间尺度由热 X 射线日冕的直接发射和吸积盘内边缘的再处理发射之间的光传播路径设置^3,4,5,6. 然而，黑洞质量、内圆盘半径和圆盘上方照明日冕高度之间的混响信号存在固有的简并性。在这里，我们使用高度可变的活跃星系 IRAS 13224-3809 的长 X 射线观测来跟踪系统在一天^7,8的时间尺度上演化时的混响信号。考虑到所有相对论效应，建模显示 X 射线日冕的高度随着光度的增加而增加，从而提供了内部吸积区域的动态视图。这种同步建模使我们能够打破固有的简并性，并获得对黑洞质量和自旋的独立的基于时间的估计。黑洞质量的不确定性与领先的光学混响方法相当⁹，使 X 射线混响成为一项强大的技术，特别是对于具有低光学可变性的光源¹⁰。