The energy released from accretion on to a supermassive black hole has significant implications for the evolution of its host galaxy. Much of this energy is released in the form of radiative feedback that is concentrated within a few tens of gravitational radii from the central black hole. Therefore studying the inner accretion flow—at the intersection of infall and outflow—is essential for understanding how the feedback mechanism works and the effect it will have on the surrounding environment.
The aim of my research is to understand these extreme, relativistic environments through observations of X-ray reverberation mapping. Similar to Optical reverberation mapping, where time delays of days or weeks between the continuum and the emission lines from scattered light in Broad Line Region clouds map out kiloparsec scales, X-ray reverberation reveals time delays of tens of seconds, which map out submicroparsec scales in the accretion flow—well beyond the spatial resolution power of any instrument. This technique has just been discovered in the past 6 years, so in this talk I will give an overview of how the measurements are taken, and the discoveries and advancements in this quickly developing field. I will show how reverberation is breaking degeneracies in our physical models and how it is helping us understand the geometry and kinematics of the inner accretion flow with unprecedented sensitivity.