Microlens Diagnostics of Accretion Disks in Active Galactic Nuclei

Abstract

The optical-ultraviolet continuum from active galactic nuclei (AGN) seem to originate from optically thick and/or thin disks, and occasionally from associated circumnuclear starburst regions. These different possible origins can, in principle, be discriminated by observations of gravitational microlensing event. We performed numerical simulations of microlensing of an AGN disk by a single lensing star passing in front of the AGN. Calculated spectral variations and light curves show distinct behavior, depending on the nature of emitting region; the time variation of a few months with strong wavelength dependence is expected in the case of an optically thick disk ({\it standard disk}), while an optically thin disk ({\it advection-dominated disk}) will produce shorter, nearly wavelength-independent variation. In the case of a starburst region much slower variations (over a year) will be superposed on the shorter variations.