# New structures of Power Density Spectra for four Kepler AGNs

## TL;DR

This study analyzes Kepler data of four AGNs, revealing multiple characteristic frequencies in their power spectra and supporting models of accretion-related variability mechanisms.

## Contribution

It identifies multiple break frequencies in AGN power spectra and links them to accretion processes, providing new insights into AGN variability structures.

## Key findings

- Two characteristic break frequencies at log(f/Hz)=-5.2 and -4.7
- Detection of similar features in X-ray data for one AGN
- Evidence supporting multiplicative variability models

## Abstract

Many nearby AGNs display a significant short-term variability. In this work we re-analyze photometric data of four active galactic nuclei observed by Kepler in order to study the flickering activity, having as main goal that of searching for multiple components in the power density spectra. We find that all four objects have similar characteristics, with two break frequencies at approximately log(f/Hz)=-5.2 and -4.7. We consider some physical phenomena whose characteristic time-scales are consistent with those observed, in particular mass accretion fluctuations in the inner geometrically thick disc (hot X-ray corona) and unstable relativistic Rayleigh-Taylor modes. The former is supported by detection of the same break frequencies in the Swift X-ray data of ZW229-15. We also discuss rms-flux relations, and we detect a possible typical linear trend at lower flux levels. Our findings support the hypothesis of a multiplicative character of variability, in agreement with the propagating accretion fluctuation model.