KEPLER OBSERVATIONS OF RAPID OPTICAL VARIABILITY IN ACTIVE GALACTIC NUCLEI

Over three quarters in 2010–2011, Kepler monitored optical emission from four active galactic nuclei (AGNs) with ∼30 minute sampling, >90% duty cycle, and ≲0.1% repeatability. These data determined the AGN optical fluctuation power spectral density (PSD) functions 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 AGNs exhibit intrinsically different PSD slopes. The steep PSD fits are a challenge to recent AGN variability models but seem consistent with first-order magnetorotational instability theoretical calculations of accretion disk fluctuations.