Speaker
Description
Although flux variability is one of the fundamental properties of accretion flows onto supermassive black holes, its dependence on physical parameters such as the mass of the compact object and the Eddington ratio are still debated. In this contribution I will present new observational constraints on the Power Spectral Density (PSD) of the X-ray variability of Active Galactic Nuclei as a function of black hole mass and Eddington ratio. Multi-epoch eROSITA data are combined with archival XMM observations of SDSS QSOs to infer the ensemble (averaged over populations) normalised excess variance and the corresponding ensemble PSD in bins of black hole mass and Eddington ratio. The analysis is based on a new Bayesian methodology that correctly accounts for the Poisson nature of X-ray observations and allows maximal information gain from light curves. Preliminary results suggest an unexpectedly complex dependence of the variability on Eddington ratio. It is found that the amplitude of the X-ray flux variations increases close to the Eddington limit, in stark contrast to expectations based on moderate luminosity Seyferts, for which an anti-correlation of the variability amplitude and Eddington ratio is suggested in the literature. I will discuss this result in the context of different physical models for the feeding and feedback cycle of the fast accreting supermassive black holes.
