We present multi-frequency VLBA+VLA observations of SS433 at 1.6, 5 and 15
GHz. These observations provide the highest angular resolution radio spectral
index maps ever made for this object. Motion of the components of SS433 during
the observation is detected. In addition to the usual VLBI jet structure, we
detect two radio components in the system at an anomalous position angle. These
newly discovered radio emitting regions might be related to a wind-like
equatorial outflow or to an extension of the accretion disk. We show that the
radio core component is bifurcated with a clear gap between the eastern and
western wings of emission. Modelfitting of the precessing jets and the moving
knots of SS433 shows that the kinematic centre -- i.e. the binary -- is in the
gap between the western and eastern radio core components. Spectral properties
and observed core position shifts suggest that we see a combined effect of
synchrotron self-absorption and external free-free absorption in the innermost
AU-scale region of the source. The spatial distribution of the ionized matter
is probably not spherically symmetric around the binary, but could be
disk-like.Comment: Accepted for publication by Astronomy and Astrophysic
