The Case for Standard Irradiated Accretion Disks in Active Galactic Nuclei

TL;DR

This study supports the standard irradiated accretion disk model for optical emission in low-luminosity AGN by analyzing light curves and measuring time delays consistent with theoretical predictions.

Contribution

It provides the first robust observational evidence that optical lags in Seyfert galaxies align with standard accretion disk models, supporting their role in AGN emission.

Findings

Detected propagating perturbations across continuum regions.

Measured reliable inter-band time delays unaffected by emission lines.

Found lag measurements consistent with irradiated disk predictions.

Abstract

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.