The central X-ray source in SS 433

Numerous observations of SS 433 were obtained with the Einstein X-ray Observatory over an 18 month period from 1979 March through 1980 October. MPC (as well as imaging) data from these observations show that the central object in SS 433 is variable in intensity and spectrum on a wide range of time scales. Flares appear to be correlated with the 13 day binary period, and may be more numerous at particular phases of the 164 day period. No evidence for variability on time scales less than 5 minutes is seen, suggesting the central X-ray source is extended and that the compact object itself is not directly visible. A model for SS 433 is suggested wherein the companion star has a spin misaligned with the orbital angular momentum. The volume of the Roche lobe reaches a minimum twice per binary orbit, giving rise to enhanced accretion which results in X-ray and radio flares. Additional constraints imposed by the X-ray and optical data suggest the compact object in SS 433 is an approximately 10-solar-mass black hole.