2014A&A...562A..81R

We analyzed Suzaku data of the black hole candidate 4U 1630-472 when it was in the high/soft state. The source, known for X-ray outbursts and for absorption dips, has an X-ray continuum spectrum that is interpreted correctly as emission from an accretion disk. Additionally, two absorption lines from He and H-like iron have been clearly detected in the high-resolution data from 4U 1630-472. We show that the continuum X-ray spectrum of 4U 1630-472 with iron absorption lines can be satisfactorily modeled by the spectrum from an accretion disk atmosphere. Absorption lines of highly ionized iron originating in a hot accretion-disk atmosphere can be an alternative or complementary explanation to the wind model usually favored for this type of sources. We performed full radiative transfer calculations to model the emission from an accretion disk surface that is seen at different viewing angles using our transfer code ATM21. Computed models are then fitted to high-resolution X-ray spectra of 4U 1630-472 obtained by the Suzaku satellite. We modeled continuum and line spectra using a single model. Absorption lines of highly ionized iron can originate in the upper parts of the disk atmosphere, which is intrinsically hot because of the high disk temperature. Iron line profiles computed with natural, thermal, and pressure broadenings match observations very well. According to any global disk models considered for the mass of central object that is close to 10M_☉ or less, the effective temperature of the inner radii reaches 10⁷K. We showed that the accretion disk atmosphere can effectively produce iron absorption lines observed in 4U 1630-472 spectrum. Absorption line arising in an accretion disk atmosphere is the important part of the observed line profile, even if there are also other mechanisms responsible for the absorption features. Nevertheless, the wind theory can be an artefact of the fitting procedure when the continuum and lines are fitted as separate model components.