Recent X-ray observations of active galactic nuclei with ASCA suggest that we may be observing Fe-K line emission from very close to the central black-black hole. We provide here the relevant formalism to interpret those observations. We show how to model the appearance of an accretion disk around a rotating black hole and line profiles from disk emission. We try to present in a coherent way results that are scattered in the litterature and/or that are limited to particular cases. We extend these results to the more general case of a rotating black hole (Kerr metric). We finally discuss the relation of the full width at zero intensity of the line to the angular momentum of the black hole.

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Abstract. An efficient numerical code to calculate line profiles from warped disks around nonrotating black holes is presented. Extensive numerical experiments suggest a method making it possible to distinguish between line profiles belonging to flat and warped accretion disks. The extension of our code to rotating black holes is briefly discussed.