Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei

TL;DR

This study uses Kepler data to analyze optical variability in four AGNs, revealing steep power spectral density slopes that challenge existing models but align with MRI disk fluctuation theories.

Contribution

It provides the first detailed optical PSD measurements of AGNs over a wide frequency range using Kepler, highlighting variability differences and theoretical implications.

Findings

Steep PSD slopes between -2.6 and -3.3 in optical band

Evidence of intrinsic variability differences among AGNs

Steep PSDs challenge existing variability models but support MRI-based theories

Abstract

Over three quarters in 2010-2011, Kepler monitored optical emission from four active galactic nuclei (AGN) with ~30 min sampling, >90% duty cycle, and <~0.1% repeatability. These data determined the AGN optical fluctuation power spectral density functions (PSDs) over a wide range in temporal frequency. Fits to these PSDs yielded power law slopes of -2.6 to -3.3, much steeper than typically seen in the X-rays. We find evidence that individual AGN exhibit intrinsically different PSD slopes. The steep PSD fits are a challenge to recent AGN variability models but seem consistent with first order MRI theoretical calculations of accretion disk fluctuations.