Probing the history of SS433's jet kinematics via decade-resolution radio observations of W50

We present the results of a kinematical study of the W50 nebula using high-resolution radio observations from the Very Large Array spanning a 12-yr period, sampled in 1984, 1993 and 1996. We conduct a careful analysis of the proper motions of the radio filaments across the W50 nebula at each epoch and detect no significant motion for them during this period. The apparent lack of movement in the radio filaments mandates either (i) a high degree of deceleration of SS433's jet ejecta in the W50 nebula; or (ii) that the lobes of W50 formed a long time ago in SS433's history, during a jet outburst with appreciably different characteristics from the well-known precessing jet state observed in SS433 at the present day. We discuss the possible scenarios which could explain this result, with relevance to the nature of SS433's current jet activity. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS