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 similar to 30 degrees. From the thermal emission of the eastern X-ray lobe, we determine a pressure of P similar to 3 x 10(-11) erg/cm(3) 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 similar to 100 000 yr ago. Also, this pressure in our entrainment model gives a deceleration of the jet by similar to 60% in the bounds of the spherical component of W 50, of radius similar to 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 sigma = alpha P, where the viscosity parameter alpha is predefined by the model.