The relativistic shift of narrow spectral features from black-hole accretion discs
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Transient spectral features have been discovered in the X-ray spectra of Active Galactic Nuclei, mostly in the 5--7 keV energy range. Several interpretations were proposed for the origin of these features. We examined a model of Doppler boosted blue horns of the iron line originating from a spot in a black hole accretion disc, taking into account different approximations of general relativistic light rays and the resulting shift of energy of photons. We provide a practical formula for the blue horn energy of an intrinsically narrow line and assess its accuracy by comparing the approximation against an exact value, predicted under the assumption of a planar accretion disc. The most accurate approximation provides excellent agreement with the spot orbital radius down to the marginally stable orbit of a non-rotating black hole.
Accepted for publication in A&A; 8 pages, 5 figures
Accepted for publication in A&A; 8 pages, 5 figures