The spectrum of an accretion disk around a rotating black hole

Broad emission lines are observed in the X-ray spectra of Seyfert galaxies. These lines may be formed in the inner part of the accretion disk, where t he effects of general relativity must be taken into account. In this contex t, we consider the structure of individual spectral lines emitted by a "hot spot" moving in a Kerr accretion disk along a geodesic trajectory in the e quatorial plane as a function of the radial coordinate r of the spot and th e specific angular momentum a = J/M of the black hole. A characteristic two -peaked line profile with steep wings is formed at relatively large distanc es of about (3-10)r(g) from the black hole. Lines observed from the inner r egion have a single peak and a very broad red wing. High-accuracy observati ons of spectral-line profiles could provide information on the specific ang ular momentum a of the black hole.