Scattering of X-ray emission lines by the neutral and molecular hydrogen   in the Sun's atmosphere and in the vicinity of active galactic nuclei and   compact sources
  In many astrophysical objects an account for scattering of the X-ray fluorescent and resonance lines of iron ions by the electrons, bound in atomic and molecular hydrogen is important. Specific distortions of the scattered line profile spectrum appear in comparison with scattering by free electrons. Analysis of scattered line spectra may provide information on the ionization state, helium abundance and geometry of scattering media in the vicinity of AGNs, compact X-ray sources and on the surface of X-ray flaring stars and the Sun. 
R.Sunyaev (MPI fur Astrophysik, Garching bei Munchen, Germany),   E.Churazov (Space Research Institute, Moscow, Russia)