Magnetic field estimation in Cyg X-3's jet
  Multi-wavelength photometric observations of Cygnus X-3 were carried out at 18 cm through to 450 um, complemented by X-ray (2-10 keV) observations. The system was mildly active with cm fluxes at 150 -- 250 mJy. We find the spectrum to be flat with a spectral index of zero. Using a modified Wolf-Rayet wind model, and assuming emission is generated in synchrotron emitting jets from the source, we find an upper-limit to the magentic field of 20 G at a distance of $5 \times 10^{12}$ cm is required. 
R.N. Ogley, S.J. Bell Burnell, R.P. Fender, G.G. Pooley, E. B.   Waltman, M. van der Klis