The Case for Standard Irradiated Accretion Disks in Active Galactic
  Nuclei
  We analyze the broadband photometric light curves of Seyfert 1 galaxies from
the Sergeev et al. (2005) sample and find that a) perturbations propagating
across the continuum emitting region are a general phenomenon securely detected
in most cases, b) it is possible to obtain reliable time-delays between
continuum emission in different wavebands, which are not biased by the
contribution of broad emission lines to the signal, and that c) such lags are
consistent with the predictions of standard irradiated accretion disk models,
given the optical luminosity of the sources. These findings provide new and
independent support for standard accretion disks being responsible for the bulk
of the (rest) optical emission in low-luminosity active galactic nuclei (AGN).
We interpret our lag measurements in individual objects within the framework of
this model and estimate the typical mass accretion rate to be <~0.1Msol/yr,
with little dependence on the black hole mass. Assuming bolometric corrections
typical of type-I sources, we find tentative evidence for the radiative
efficiency of accretion flows being a rising function of the black hole mass.
With upcoming surveys that will regularly monitor the sky, we may be able to
better quantify possible departures from standard self-similar models, and
identify other modes of accretion in AGN.
