A prolonged injection jet model for the radio bursts of blazars

In order to interpret the general evolutional properties of radio bursts in blazars a prolonged injection jet model is proposed. It is assumed that relativistic plasma containing magnetic field and relativistic electrons is injected over a prolonged period at relativistic speeds into the base of the jet, which then expands adiabatically as it moves outward along the jet axis. Calculations show that the spectral evolution of radio bursts has the 3-stage pattern suggested by Valtaoja et al. and reproduce well the general behaviour of the bursts