Investigating Non-linear and Stochastic Hard X-ray Variability of Active Galactic Nuclei using Recurrence Analysis by R. A. Phillipson et al. on Sunday 27 November

We present results of recurrence analysis of 46 active galactic nuclei (AGN)

using light curves from the 157-month catalog of the Swift Burst Alert

Telescope (BAT) in the 14-150 keV band. We generate recurrence plots and

compute recurrence plot metrics for each object. We use the surrogate data

method to compare all derived recurrence-based quantities to three sets of

stochastic light curves with identical power spectrum, flux distribution, or

both, in order to determine the presence of determinism, non-linearity,

entropy, and non-stationarity. We compare these quantities with known physical

characteristics of each system, such as black hole mass, Eddington ratio, and

bolometric luminosity, radio loudness, obscuration, and spectroscopic type. We

find that almost all AGN in this sample exhibit substantial higher-order modes

of variability than is contained in the power spectrum, with approximately half

exhibiting nonlinear or non-stationary behavior. We find that Type 2 AGN are

more likely to contain deterministic variability than Type 1 AGN while the same

distinction is not found between obscured and unobscured AGN. The complexity of

variability among Type 1 AGN is anticorrelated with Eddington ratio, while no

relationship is found among Type 2 AGN. The connections between the recurrence

properties and AGN class suggest that hard X-ray emission is a probe of

distinct accretion processes among classes of AGN, which supports

interpretations of changing-look AGN and challenges the traditional unification

model that classifies AGN only on viewing angle.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.13774v1