On the influence of resonant absorption on the iron emission-line profilesfrom accreting black holes

The fluorescent iron K alpha emission-line profile provides an excellent pr obe of the innermost regions of active galactic nuclei. Fe xxv and Fe xxvi in diffuse plasma above the accretion disc can affect the X-ray spectrum by iron K alpha resonant absorption. This in turn can influence the interpret ation of the data and the estimation of the accretion disc and black hole p arameters. We embark on a fully relativistic computation of this effect and calculate the iron line profile in the framework of a specific model in wh ich rotating, highly ionized and resonantly absorbing plasma occurs close t o the black hole. This can explain the features seen in the iron K alpha li ne profile recently obtained by Nandra et al. for the type 1 Seyfert galaxy NGC 3516. We show that the redshift of this feature can be mainly gravitat ional in origin and accounted for without the need to invoke fast accretion of matter on to the black hole. New X-ray satellites such as XMM, ASTRO-E and Chandra provide excellent opportunities to test the model against high- quality observational data.