1999A&A...343...41Y

The optical-ultraviolet continuum from active galactic nuclei (AGN) seems to originate from optically thick and/or thin disks, and occasionally from associated circumnuclear starburst regions. These different possible origins can, in principle, be distinguished by observations of gravitational microlensing events. 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 the emitting region; time variation over few months with strong wavelength dependence is expected in the case of an optically thick disk (standard disk), while an optically thin disk (advection-dominated disk) will produce shorter, nearly wavelength-independent variation. In the case of an associated circumnuclear starburst region much slower variations (over a year) will be superposed on the shorter variations caused by microlensing of the disk.