New evidence at X-ray and COS-B gamma-ray frequencies for non-thermalphenomena in Wolf-Rayet stars.

The relativistic electrons responsible for the non-thermal radio emission of some Wolf-Rayet stars probably also generate high levels of inverse-Compton X-rays and bremsstrahlung γ-rays. Of the six stars of this type recognised by Abbott et al. (1986) out of a distance-limited sample of forty Wolf-Rayet stars HD 193793 is an exceptionally bright X-ray source and is also one of four stars which may be COS-B γ-ray sources. The 1977 infrared outburst of HD 193793 may have been non-thermal synchrotron emission from deep within the wind rather than dust condensation. Simultaneous observations of objects of this type at different frequencies allow the magnetic field to be constrained. HD 193793 probably has a surface field near 200 G.