The Kepler Light Curves of AGN: A Detailed Analysis

TL;DR

This study analyzes 21 Kepler light curves of Type 1 AGN, revealing diverse variability behaviors, characteristic timescales linked to black hole mass, and correlations between luminosity and variability, with implications for accretion processes.

Contribution

It introduces a customized pipeline for Kepler AGN data and provides detailed variability analysis, including PSD features and flux behavior, not previously explored in optical wavelengths.

Findings

PSD flattening correlates with black hole mass.

Luminosity is anticorrelated with variability and PSD slope.

No evidence of linear rms-flux relationships or lognormal flux distributions.

Abstract

We present a comprehensive analysis of 21 light curves of Type 1 AGN from the Kepler spacecraft. First, we describe the necessity and development of a customized pipeline for treating Kepler data of stochastically variable sources like AGN. We then present the light curves, power spectral density functions (PSDs), and flux histograms. The light curves display an astonishing variety of behaviors, many of which would not be detected in ground-based studies, including switching between distinct flux levels. Six objects exhibit PSD flattening at characteristic timescales which roughly correlate with black hole mass. These timescales are consistent with orbital timescales or freefall accretion timescales. We check for correlations of variability and high-frequency PSD slope with accretion rate, black hole mass, redshift and luminosity. We find that bolometric luminosity is anticorrelated with both variability and steepness of the PSD slope. We do not find evidence of the linear rms-flux relationships or lognormal flux distributions found in X-ray AGN light curves, indicating that reprocessing is not a significant contributor to optical variability at the 0.1-10% level.