FEATURES OF THE FLUORESCENT IRON LINE FROM HIGHLY INCLINED DISKS - SOME POSSIBLE EXAMPLES FOR NGC-6814

The fluorescent iron line (at 6-7 KeV) is now widely regarded as a basic feature of the X-ray spectra of active galactic nuclei (AGNs) and Galactic black hole candidates. Rapid variability of the iron line suggests its origin from the inner regions of the accretion disk, which therefore may throw light on the physics of the nucleus. In this Letter, we report some important properties of the line profiles due to a highly inclined disk, making the implication that NGC 6814 can serve as a target for investigating the line properties, which is of great importance astrophysically as it may provide some direct evidence for the existence of a black hole in the nucleus of NGC 6814. Apart from the famous double horns in the line profile, another feature has been noticed between the two horns, which is accounted for by the close vicinity of the trajectory of the observed X-ray photons from the disks with a high inclination angle to the central black hole. The photons are strongly lensed by the central black hole, thus producing the ''extra'' feature between the two horns as a result of the Doppler shift. A highly inclined system is most probably self-eclipsed by the outer part of the disk. The natural width and strength of the line are both subject to the eclipse. Since NGC 6814 is considered to have a very high inclination within the hot spot model, its narrow k(alpha) line can, therefore, be explained in terms of the accretion disk self-eclipse.