Hydrodynamical models of superluminal sources

We present numerical simulations of the generation, evolution, and radio emission of superluminal components in relativistic jets. We perform the fluid dynamical calculations using a relativistic time-dependent code based on a high-resolution shock-capturing;scheme, and then we calculate the radio emission by integrating the transfer equations for synchrotron radiation. These simulations show that a temporary increase in the flow velocity at the base of the jet produces a moving perturbation that contains both a forward and a reverse shock and is trailed by a rarefaction. The perturbation appears in the simulated maps as a region of enhanced emission moving downstream at a superluminal apparent velocity. Interactions of the perturbation with the underlying steady jet result in changes in the internal brightness distribution of the superluminal component, which are manifested as low-level fluctuations about the long-term evolution of both the apparent velocity and the exponential decay of the light curves.