Large-scale superluminal motion in the quasar 3C273

The quasar 3C273, one of the first discovered, is optically the brightest example of a source with a one-sided jet. It was also the first object to display apparent superluminal motion on parsec scales, a phenomenon attributed to relativistic effects on the appearance of a jet moving close to the line of sight. The same explanation allows an intrinsically similar 'counter-jet', moving at high speed in the opposite direction, to be dimmed to invisibility. We have made observations at 1.7 GHz, using very-long-baseline interferometry with a global network of 16 radiotelescopes, resulting in a high-dynamic-range map of the jet with a ratio of peak brightness to r.m.s. noise level of 16,000:1. We fail to see a counter-jet, a result which is just barely consistent with the standard model of a superluminal jet. The jet extends out to 220 pc, and some models require that the relativistic bulk flow should continue along its entire length. Comparison with an earlier image shows that superluminal motion extends out to at least 120 pc, three times farther than previously noted. Because different components emerge with different velocities, a third epoch of observations is needed to determine if any deceleration has occurred.