Jets of SS 433 on scales of dozens of parsecs

Context. The radio nebula W 50 harbours the relativistic binary system SS 433, which is a source of powerful wind and jets. The origin of W 50 is wrapped in the interplay of the wind, supernova remnant, and jets. The evolution of the jets of SS 433 on the scale of the nebula W 50 is a Rosetta stone for its origin.
Aims: To disentangle the roles of these components, we study the physical conditions of the propagation of the jets of SS 433 inside W 50 and determine the deceleration of the jets.
Methods: We analysed the morphology and parameters of the interior of W 50 using the available observations of the eastern X-ray lobe, which trace the jet. In order to estimate deceleration of this jet, we devised a simplistic model of the viscous interaction of a jet, via turbulence, with the ambient medium. This model fits mass entrainment from the ambient medium into the jets of the radio galaxy 3C 31, the well-studied case of continuously decelerating jets.
Results: X-ray observations suggest that the eastern jet is hollow, persists through W50, and is recollimated to the opening angle of 30°. From the thermal emission of the eastern X-ray lobe, we determine a pressure of P 3 × 10^-11 erg/cm³ inside W 50. In the frame of a theory of the dynamics of radiative supernova remnants and stellar wind bubbles, in combination with other known parameters this pressure restricts the origin of W 50 to a supernova occuring 100 000 yr ago. Also, this pressure in our entrainment model gives a deceleration of the jet by 60% in the bounds of the spherical component of W 50, of radius 40 pc. In this case, the age of the jet should be ≪27 000 yr so as to satisfy the sphericity of W 50. The entrainment model comes to the viscous stress in a jet of a form σ = αP, where the viscosity parameter α is predefined by the model.