Diffuse X-ray emission from the jets of SS433

Abstract

The discovery of strong, variable emission lines¹, which are Doppler-shifted² from SS433, led to the development of a kinematic beam model^3–5 which explains the principal features of the time varying optical spectrum. In this model two opposed jets of material moving outwards from the central star at 0.258c precess with a period of 164 days, about an axis inclined 80° (or 20°) to the line of sight of the observer. The locus of the two beams forms a cone with an opening half angle of 20° (or 80°) (in the model an ambiguity exists between the inclination and cone angles, as the optical data alone cannot distinguish between the two possibilities). A 13-day period observed in the velocity of the ‘stationary’ lines from this object⁶ shows that the system is binary. However, other models exist which also account for the time varying optical spectrum. For example, one model suggests that the Doppler-shifted emission lines originate in a ring of material orbiting a solitary massive black hole⁷. We now report the detection of large-scale X-ray ‘jets’ from SS433. The X-ray emission is diffuse, extending at least 30 arc min from SS433, and is exactly aligned with both SS433 and the bulges of the shell of the huge supernova remnant (SNR) W50. This detection now (1) directly confirms the existence of jets related to SS433, (2) shows the link between SS433 and W50, proving that SS433 is galactic, (3) establishes a minimum age of the jet phenomenon of ∼10³ yr, and (4) offers an explanation of why W50 is so much larger than any other known SNR in at least one dimension. The morphology of the diffuse X-ray emission is strikingly similar to that of radio lobes of many extragalactic sources; either in situ heating or particle acceleration is required to explain the appearance of the diffuse X-ray emission.