The comparison of the relativistic iron line models

Abstract

The analysis of the broad iron line profile in the X-ray spectra of active galactic nuclei and black hole X-ray binaries allows us to constrain the spin parameter of the black hole. We compare the constraints on the spin value for two X-ray sources, MCG-6-30-15 and GX 339-4, with a broad iron line using present relativistic line models in XSPEC -LAOR and KYRLINE. The LAOR model has the spin value set to the extremal value a = 0.9982, while the KYRLINE model enables direct fitting of the spin parameter. The spin value is constrained mainly by the lower boundary of the broad line, which depends on the inner boundary of the disk emission where the gravitational redshift is maximal. The position of the inner disk boundary is usually identified with the marginally stable orbit which is related to the spin value. In this way the LAOR model can be used to estimate the spin value. We investigate the consistency of the LAOR and KYRLINE models. We find that the LAOR model tends to overestimate the spin value. However, the discrepancies between results of both models are within the general uncertainties when applied on the current data.