W50 morphology and the dynamics of SS 433 formation

The jets of SS 433 have punched through the supernova remnant from the explosion forming the compact object. The precessing jets collimate before reaching beyond the shell, some 40 pc downstream, just the region of origin of TeV gamma radiation. Collimation could be effected by ambient pressure in the SNR cavity; I investigate conditions under which W50 morphology and the origins of TeV gamma radiation can be explained in terms of collimation, with associated shocks, induced by ambient pressure. I consider the age of the SNR and hence the present ambient pressure. The cavity is now ~ 10^5 years after the supernova; with lower pressure, collimation and associated shocks would occur ~40 pc downstream, just the origin of TeV gamma radiation. Modelling of evolution of binary systems indicates that Roche lobe overflow and initiation of the jets is recent. Collimation would still occur ~40 pc downstream, but the cone angle of the precession must then have increased with time - driven by the Roche lobe overflow. The morphology of W50 and the site of the origin of TeV gamma radiation are readily explained in terms of collimation of the jets by internal SNR pressure.