Exploring the Jet Proper Motions of SS433

SS433, an X-ray binary located in the constellation Aquila and the supernova remnant W50, has been studied extensively in the radio and optical for over 20 years. The currently accepted model was developed to explain the moving optical lines, and also fits very well the morphology of the twin precessing radio jets. SS 433 is the one case for which the outflow velocity in the jet (0.26c) is determined by Doppler shifted line emission. We analyzed a sequence of images from 40 daily VLBA observations at 1.4 GHz of SS 433, to study the kinematics of bright radio-emitting regions in the jet outflow. The motion of 8 pairs of ejected blobs can be followed for 40 days in this unprecedented data set spanning one quarter of a precession cycle of 164 days. We demonstrate clearly that the apparent velocities of individual components deviate from the kinematic model by more than 10 percent, even though the model still fits the radio morphology on scales of 50-500 AU. This means the radio emission does not trace the ballistic flow of material, but rather the motion of an overlying pattern of enhanced density, magnetic field or shocks in the jet.

This research was supported by the National Radio Astronomy Observatory Summer Student program, with partial support from the National Science Foundation.