The cauldron at the core of SS 433

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Abstract
We propose that the jets in SS 433 are accelerated just outside the magnetopause of a magnetized neutron star. Although the escape speed from this radius is subrelativistic, the jets are able to attain a nearly relativistic speed by passing through narrow de Laval nozzles, which are stabilized from below by the tension in the magnetic field. The narrowness of the nozzles accounts ultimately for the collimation of the jets. No funnel or vortex is necessary, and the gas outside the magnetopause need not be rapidly rotating. In order to be accelerated by electron scattering radiation pressure, the jets must carry a highly supercritical energy flux, L > 1039 erg s−1. This energy may be supplied by one of two processes: (1) a highly inhomogeneous shower of ‘broomsticks’ or blobs on to the surface of the neutron star; or (2) the rapid spin of the neutron star, which causes the oblique magnetosphere to drive shocks into the surrounding gas. In either case, the magnetopause defines the extent of a ‘cauldron’ within which radiant energy is violently mixed with gas settling in from outside. The weight of the slowly accreting gas determines the size of the magnetosphere. From the observed collimation and velocity of the SS 433 jets we infer the properties of the confining cloud and constrain the parameters of the energy source. We argue that the velocity of the jets should be insensitive to fluctuations in the accretion rate, in agreement with observations. The photosphere of the cloud should be a strong source of far-ultraviolet continuum, which cannot be observed directly but which may be responsible for exciting the strong ‘stationary’ emission lines.

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