Modeling the IDV emissions of the BL Lac Objects with a Langevin type   stochastic differential equation
  In this paper, we introduce a simplified model for explaining the observations of the optical intraday variability (IDV) of the BL Lac Objects. We assume that the source of the IDV are the stochastic oscillations of an accretion disk around a supermassive black hole. The Stochastic Fluctuations on the vertical direction of the accretion disk are described by using a Langevin type equation with a damping term and a random, white noise type force. Furthermore, the preliminary numerical simulation results are presented, which are based on the numerical analysis of the Langevin stochastic differential equation. 
C. S. Leung, J. Y. Wei, T. Harko, Z. Kovacs
astro-ph.HE