The Central Radio Gap and the equatorial emission region in SS433

The radio-jet X-ray binary SS433 was observed at five epochs in 1998 by the very long baseline interferometry (VLBI) technique at five frequencies ranging from 1.6 to 22 GHz. The innermost region of the source on milliarcsecond scales (I mas = 5 AU) is resolved into an eastern and a western core-jet component, well separated by the Central Radio Gap (25-30 AU projected size), where the binary stellar system is located. We suggest that the radio gap is caused by local synchrotron self-absorption and external free-free absorption in an ionized medium, which has a disk-like geometry. On 100 AU scales we observe the Equatorial Emission Region, oriented roughly perpendicularly to the jets, with variable morphology at different epochs. Both of these phenomena could be interpreted with a mass outflow from the system, concentrated in the orbital plane of the binary.