2004ApJ...616L..95Z

Accelerating superluminal motions were detected recently by multiepoch very long baseline interferometry observations. Here a linear accelerating superluminal motion (LASM) model is proposed to interpret the observed phenomena. The model provides a direct and accurate way to estimate the viewing angle of a relativistic jet. It also predicts that both Doppler boosting and deboosting effects may take place in an accelerating forward jet. The LASM model is applied to the data of the quasar 3C 273, and the initial velocity, acceleration, and viewing angle of its three components are derived through model fits. The variations of the viewing angle suggest that a supermassive black hole binary system may exist in the center of 3C 273. The gap between the inner and outer jet in some radio-loud active galactic nuclei my be explained in terms of Doppler deboosting effects when the components accelerate to ultrarelativistic speed.