PARSEC-SCALE SYNCHROTRON EMISSION FROM HYDRODYNAMIC RELATIVISTIC JETSIN ACTIVE GALACTIC NUCLEI

We present the first numerical simulations of the parsec-scale synchro tron emission from hydrodynamic relativistic jets. The jet structure i s calculated using a relativistic time-dependent hydrodynamic code bas ed on an approximate Riemann solver. The radio emission from the model jets is calculated by integrating the transfer equations of the synch rotron radiation, accounting for the appropriate opacity and relativis tic effects, such as Doppler boosting and relativistic aberration. In order to study the influence of the external medium, we present two hy drodynamical jet simulations: one with a constant external pressure, a nd a second model with a decreasing external pressure. Multifrequency radio images of the synchrotron emission from these flows are presente d, showing the existence of stationary quasi-periodic knots associated with internal oblique shocks. Whereas for the model with constant ext ernal pressure the knots remain almost constant in intensity and even in spacing, the model with decreasing external pressure shows stationa ry knots of progressively lower intensity and wider spacing as a funct ion of distance down the jet.