Speaker
Description
Active Galactic Nuclei (AGN) serve as cosmic laboratories for probing extreme physics around supermassive black holes (SMBHs). The X-ray spectra of AGN exhibit an excess in flux above the base power-law continuum at energies below 2 keV, known as the soft excess. In addition, reverberation studies find low-frequency positive lags between the soft (0.3–1 keV) and hard (4–7.5 keV) X-ray bands. A promising model for the soft excess is Comptonization of disc photons by a warm corona located near the surface of the inner accretion disc, but its variability properties are unknown. Here, we present the variability signatures of a fluctuating warm corona by solving the time-dependent radiative transfer equation and examine how its properties shape the observed lag spectrum and power spectral density across the soft and hard X-ray bands. Our results lay the groundwork for interpreting current and future X-ray timing observations of AGN in the context of a dynamic, fluctuating warm corona.