Microlens diagnostics of accretion disks in active galactic nuclei

The optical-ultraviolet continuum from active galac- tic nuclei (AGN) seems to originate from optically thick and/or thin disks, and occasionally from associated circumnuclear star- burst 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 dis- tinct behavior, depending on the nature of the emitting region; time variation over few months with strong wavelength depen- dence 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.