Composite profile of the Fe K$\alpha$ spectral line emitted from a
  binary system of supermassive black holes
  We used a model of a relativistic accretion disk around a supermassive black
hole (SMBH), based on ray-tracing method in the Kerr metric, to study the
variations of the composite Fe K$\alpha$ line emitted from two accretion disks
around SMBHs in a binary system. We assumed that the orbit of such a binary is
approximately Keplerian, and simulated the composite line shapes for different
orbital elements, accretion disk parameters and mass ratios of the components.
The obtained results show that, if observed in the spectra of some SMBH
binaries during their different orbital phases, such composite Fe K$\alpha$
line profiles could be used to constrain the orbits and several properties of
such SMBH binaries.
