Flashing superluminal components in the jet of the radio galaxy 3C120

A 16-month sequence of radio images of the active galaxy 3C120 with the Ver y Long Baseline Array reveals a region in the relativistic jet where superl uminal components flash on and off over time scales of months, while the po larization angle rotates. This can be explained by interaction between the jet and an interstellar cloud Located about 8 parsecs from the center of th e galaxy. The cloud, which rotates the polarization direction and possibly eclipses a section of the jet, represents a "missing link" between the ultr adense broad-emission-line clouds closer to the center and the Lower densit y narrow-emission-line clouds seen on kiloparsec scales.