SIMULATED VLBI IMAGES FROM RELATIVISTIC HYDRODYNAMIC JET MODELS

A series of simulated maps showing the appearance in total intensity o f flows computed using a recently developed relativistic hydrodynamic code (Duncan & Hughes) are presented. The radiation transfer calculati ons were performed by assuming that the flow is permeated by a magneti c field and fast particle distribution in energy equipartition, with e nergy density proportional to the hydrodynamic energy density (i.e., p ressure). We find that relativistic flows subject to strong perturbati ons exhibit a density structure consisting of a series of nested bow s hocks, and that this structure is evident in the intensity maps for la rge viewing angles. However, for viewing angles less than 30 degrees, differential Doppler boosting leads to a series of knots of emission t hat lie along the jet axis, similar to the pattern exhibited by many V LBI sources. The appearance of VLBI knots is determined primarily by t he Doppler boosting of parts of a more extended flow. To study the evo lution of a perturbed jet, a time series of maps was produced, and an integrated flux density light curve created. The light curve shows fea tures characteristic of a radio-loud AGN: small-amplitude variations a nd a large outburst. We find that in the absence of perturbations, jet s with a modest Lorentz factor (similar to 5) exhibit complex intensit y maps, while faster jets (Lorentz factor similar to 10) are largely f eatureless. We also study the appearance of kiloparsec jet-counterjet pairs by producing simulated maps at relatively large viewing angles; we conclude that observed hot spot emission is more likely to be assoc iated with the Mach disk than with the outer bow shock.