Testing the mechanisms for optical micro-variability of powerful active galactic nuclei

Abstract

We present the first results of a new type of observational program being carried out using the 2.34m Vainu Bappu Telescope at Kavalur. This program involves intra-night optical monitoring of radio quiet but optically luminous quasars. This experiment is expected to provide a fairly straight-forward test of the two major mechanisms that have been proposed so far to explain the phenomenon of optical micro-variability of powerful active galactic nuclei (AGN), which has been established during the past 4 years. The two categories of mechanisms involve (1) shocks moving in the relativistic jets and (2) random hot spots occurring on the quasar accretion disks. Our optical monitoring of the 7 radio-quiet quasars, so far, has not revealed any clear event of intra-night variability. Positive detection of such a variability would provide a strong support to the model invoking accretion disks, while a clear absence of such events would strongly favor the models relying on shocks propagating down the relativistic jets.