THE JETS AND HOTSPOTS OF 3C-390.3

We present high-resolution VLA images at 6 and 18 cm of the nearby classical double radio source 3C 390.3. We have discovered a faint, well-collimated jet extending from the nucleus to the northern hotspot, and a less well-defined counterjet to the south. We have mapped the distribution of Faraday rotation across the hotspots, and have used this to assess models for the asymmetric depolarization seen at long wavelengths. Our results suggest that the asymmetry is due to a larger external Faraday depth on the counterjet side, consistent with the idea that the counterjet is faint because its emission is relativistically beamed away from us. The detailed structure of the hotspots is very difficult to understand as a quasi-stationary fluid flow, but is in excellent agreement with the transient structures seen in recent numerical simulations. In the northern hotspot the jet remains well collimated for some distance after a sharp (projected) bend, and rapid brightening appears to indicate substantial dissipation of its kinetic energy and momentum flux. The same is true in the southern hotspot, if we have correctly identified the jet. We suggest that the unusual prominence of the hotspots is caused by a relatively brief episode of enhanced power in the jets, while the striking difference in their overall structure results from our observation of this episode at two different phases because of the light-travel time across the object.