Sco X-1 and Cyg X-1: Determination of Strength and Structure of Magnetic   Field in the Nearest Environment of Accreting Compact Stars
  We estimated the magnetic field strength of compact stars in X-ray binaries Sco X-1 and Cyg X-1, via various methods of determination of magnetic fields. For Sco X-1 we used three independent methods. One of them is based on the correct account of the Faraday rotation of polarization plane in the process of electron scattering of X-rays from accreting neutron stars. Numerical calculations are made with use of first X-rays polarimetric data presented by Long et al. (1979). Other original method of determing the magnetic field developed by Titarchuk at al. (2001) is based on observed quasi-periodic oscillations (QPO) frequencies in X-ray binaries that can be considered as magnetoacoustic oscillations of boundary layer near a neutron star. The optical polarimetric data obtained in 70-th have been also used for estimation of magnetic field of the neutron star in Sco X-1 and of nearest environment around the black hole in Cyg X-1. 
Yu.N. Gnedin, N.A. Silant'ev, and L.G. Titarchuk