4C 39.25: Witnessing the interaction between a moving and a stationary component

We present multi-epoch multi-frequency VLBI images of the compact polarized radio structure of the quasar 4C 39.25. Between 1995 and 1999, the total i ntensity images at 15, 22, and 43 GHz have remained almost unperturbed, whi le there have been significant changes in the polarized intensity maps toge ther with a related rotation of the polarization angle. These changes in th e polarized structure trace in great detail the interaction between a movin g and a standing component. We interpret the stationary feature as a bend i n the jet trajectory in a plane that does not contain the observer, and the moving one as a shock turning around the bend.