The radio beams on small scales

The radio emission of SS433 has been observed on several spatial scales using different radio telescopes. Radio interferometers are only sensitive to a specific range in resolution due to the design of these instruments. This means that high resolution VLBI images only show small scale structure. Large scale radio emission can only be seen with telescopes like the VLA and the WSRT.

With VLBI techniques images have been obtained down to scales of cm (1 mas). Most of the radio emission however is found on scales of cm and larger. The small features are very weak and therefore difficult to observe (Walker et al., 1981). The brightest feature in all radio maps is the core. This core is much larger than a typical binary stellar system. The radio emission is extended along the curved locus (as predicted by the kinematic model), but no resolved radio structure has been found perpendicular to this trace. Since the radio interferometers are only sensitive to a rather restricted range of spatial scales (see above) this does not give any constraines on the diameter of the beams.

Several relatively bright discrete features can be observed in VLBI maps with a resolution of cm (with a speed of this means days of travel). Also weak, more diffuse emission can be seen in maps with this resolution. Some knots (but not all) correlate with the occurance of radio flares (Vermeulen, 1989).

MERLIN observations have a typical resolution of cm (100 mas), which means about 11 days of travel at . Also on this scale the emission is not continuous. Brighter and fainter regions are observed. The evolution of the flux density of these knots has been followed by Spencer (1984). It was not clear if exponential or powerlaw fading of the knots was happening, but Spencer suggested that adiabatic expansion was indicated. The knots observed by Spencer (1984) with MERLIN were ejected from SS433 during episodes of radio flaring.

With VLA observations the lobes can be followed out to 2-3 arcsec at both sides of the core. The corresponding distance is cm (about 300 days of travel at ). These observations of SS433 show twisted lobes, which are evidence of the precessing beams. No radio emission of the beams is found at greater distances. Only the diffuse emission of W50 is seen at larger scales ( cm). (W50 is an elliptical shaped shell-like radio nebula. Although it has been classified as a supernova remnant, some authors have suggested that W50 is not the result of a supernova explosion, but the result from the blastwave connected to the stellar wind coming from SS433).

The lobes have a spectral index of , which is characteristic of optically thin synchrotron emission. On these scales the emission of SS433 usually appears continuous.