Kepler Photometry of Four Radio-Loud AGN in 2010-2012
  We have used Kepler photometry to characterize variability in four radio-loud
active galactic nuclei (three quasars and one object tentatively identified as
a Seyfert 1.5 galaxy) on timescales from minutes to months, comparable to the
light crossing time of the accretion disk around the central supermassive black
hole or the base of the relativistic jet. Kepler's almost continuous
observations provide much better temporal coverage than is possible from
ground-based observations. We report the first such data analyzed for quasars.
We have constructed power spectral densities using 8 Kepler quarters of
long-cadence (30-minute) data for three AGN, 6 quarters for one AGN and 2
quarters of short-cadence (1-minute) data for all four AGN. On timescales
longer than about 0.2-0.6 day, we find red noise with mean power-law slopes
ranging from -1.8 to -1.2, consistent with the variability originating in
turbulence either behind a shock or within an accretion disk. Each AGN has a
range of red noise slopes which vary slightly by month and quarter of
observation. No quasi-periodic oscillations of astrophysical origin were
detected. We detected several days-long flares when brightness increased by 3%
- 7% in two objects. No flares on timescales of minutes to hours were detected.
Our observations imply that the duty cycle for enhanced activity in these
radio-loud AGN is small. These well-sampled AGN light curves provide an impetus
to develop more detailed models of turbulence in jets and instabilities in
accretion disks.
