2007A&A...469L..23P

Studying the internal structure of extragalactic jets is crucial for understanding their physics. The Japanese-led space VLBI project VSOP has presented an opportunity for such studies, by reaching baseline lengths of up to 36000km and resolving structures down to an angular size of ≃0.3mas at 5GHz. VSOP observations of the jet in 0836+710 at 1.6 and 5GHz have enabled tracing of the radial structure of the flow on scales from 2mas to 200mas along the jet and determination of the wavelengths of individual oscillatory modes responsible for the formation of the structure observed. We apply linear stability analysis to identify the oscillatory modes with modes of Kelvin-Helmholtz instability that match the wavelengths of the structures observed. We find that the jet structure in 0836+710 can be reproduced by the helical surface mode and a combination of the helical and elliptic body modes of Kelvin-Helmholtz instability. Our results indicate that the jet is substantially stratified and different modes of the instability grow inside the jet at different distances to the jet axis. The helical surface mode can be driven externally, and we discuss the implications of the driving frequency on the physics of the active nucleus in 0836+710.