Speaker
Description
Accreting stellar-mass black holes in Black Hole X-ray Binaries (BHXRBs) are known to undergo distinct accretion states, likely corresponding to changes in the structure of the inner accretion flow and accompanied by strong variations in spectral energy distribution, jet production, and variability properties. These accretion states evolve during outburst cycles, with relativistic jets launched only in specific states while being suppressed in others. If analogous accretion states exist in Active Galactic Nuclei (AGN), they might provide a way to explain the diversity of AGN classes, such as radio-loud and radio-quiet systems, with important implications for AGN feedback and galaxy evolution.
A direct comparison between BHXRBs and AGN is hindered by the fact that characteristic variability timescales of accreting black holes scale linearly with black hole mass, resulting in outburst cycles lasting days to weeks in BHXRBs but orders of magnitude longer in AGN. However, in BHXRBs the shape of the X-ray variability power spectrum, quantified through the Power Spectral Density (PSD), has been shown to be closely linked to accretion state. These states exhibit distinct PSD shapes, which can be parameterised using power colours that quantify the relative variability amplitudes across different timescale ranges.
This work aims to determine the PSDs of a sample of 60 AGN X-ray light curves using PIORAN, a novel framework for fully Bayesian inference of bending power-law PSD parameters based on Gaussian processes. This approach is well suited to unevenly sampled light curves and allows the inclusion of priors on black hole mass to account for the mass-scaling of variability timescales. The inferred PSDs are analysed using their power colours to test whether AGN occupy accretion variability states analogous to those observed in BHXRB outbursts. Evidence for such similarities would support scale-invariant accretion onto black holes and has implications for AGN feedback and structure formation.
| Talk category | NOVA Network 3 |
|---|---|
| Second preference | NOVA Network 1 |
