SPIRAL SHOCKS IN ACCRETION DISKS AS A CONTRIBUTOR TO VARIABILITY IN ACTIVE GALACTIC NUCLEI

We simulate the variations in emission from accretion disks subjected to nonaxisymmetric tidal perturbations generated by masses within or passing through the disk, using a two-dimensional hydrodynamics code. Spiral shocks can form, fragment, and reform on relatively short time scales, producing variations in the optical band for accretion disks around supermassive black holes. These fluctuations may be adequate to explain much of the recently observed microvariability in BL Lacertae objects and some quasars. For short-lived encounters, substantial flaring can occur.