MULTIPLE IMAGES AND LIGHT CURVES OF AN EMITTING SOURCE ON A RELATIVISTIC ECCENTRIC ORBIT AROUND A BLACK-HOLE

The scenario of ''spots'' moving around a black hole has recently become of great interest and is considered to have important implications in astrophysics. Various studies to date have been limited to an emitting source on a circular orbit. This paper, however, presents some new results from the study of a bright source on an eccentric orbit. In the investigations, full relativistic effects are included without any approximations. Multiple images and light curves of the spot on the orbit with different parameters observed at infinity are shown. The results are then compared with those from circular orbits. It is argued that the recently revealed quasi-periodic oscillation in the X-ray emission of the Seyfert galaxy NGC 5548 can be explained in terms of a bright source on an eccentric orbit around a black hole. In addition, a method is introduced that can be applied directly in calculations of other astrophysical quantities such as the emission line from an accretion disk around a black hole or the variability power spectrum of collective ''hot spots.''