1994A&A...287..795H

We calculate the profiles and shifts of lines emitted from Keplerian accretion discs in X-ray binaries containing a neutron star or a black hole, both in the case of Schwarzschild and Kerr geometry. We give analytic approximations of the line profiles. We show that given the centroid and width of the line, one can obtain constraints on the angular momentum of the black hole and the inclination of the system. We apply these results to the electron-positron annihilation line recently discovered by SIGMA in GRS 1124-68 (nova Muscae) and 1E1740-29. We suggest that the 200keV line observed in nova Muscae could simply be the red wing of the annihilation line if the accreting object is a black hole with a/M>0.7, the inclination of the system is of the order of 40deg, and the radius of the emitting region ∼3.5M.