A statistical approach to measuring X-ray reverberation in gravitationally lensed quasars

Chandra Data Science Workshop (19/08/2021)

The measurement of X-ray reverberation around black holes, as variations in the continuum emission echo off the accretion disk, have enabled a breakthrough in mapping the extreme environments just outside the event horizon. Reverberation probes the structure of the inner accretion flow and reveals the nature of the corona that produces the X-ray continuum. Measurements of X-ray reverberation via conventional Fourier techniques, however, are limited to relatively modest supermassive black holes in nearby galaxies. Recently-developed statistical techniques, based on Gaussian processes, enable the measurement of X-ray reverberation around more massive black holes in radio galaxies by combining multiple observations to provide a longer time baseline. This framework provides a statistical basis to robustly characterize time lags in lower signal-to-noise data, enabling the measurement of X-ray reverberation in Chandra observations of gravitationally lensed quasars. X-ray reverberation measurements in lensed quasars extend our understanding to rapidly accreting black holes beyond just the local Universe and pave the way for breakthrough science with the next-generation Lynx observatory.