Disk emission and atmospheric absorption lines in black hole candidate 4U 1630-472

Abstract

Context. 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. Aims. 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. Methods. 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. Results. 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. Conclusions. According to any global disk models considered for the mass of central object that is close to 10 M or less, the effective temperature of the inner radii reaches 10 7 K. 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.

TheXMM–Newtonspectra of the 2012 outburst of the black hole candidate 4U 1630−47 revisited

“…Compared to the parameters in Kubota et al (2007), Różańska et al (2014) and Díaz Trigo et al (2014), we find a higher value of N H than theirs and the temperature of the disc is higher than that of Kubota et al (2007). The energy of the absorption lines and edges are consistent with those of Fe xxv Heα (6.70 keV), Fe xxvi Lyα (6.97 keV), Ni xxviii Lyα (8.09 keV) or Fe xxv Lyβ (7.88 keV), Fe xxvi Lyβ (8.25 keV), Fe xxv K-edge (8.83 keV) and Fe xxvi K-edge (9.28 keV), similar to the identification in Díaz Trigo et al (2014).…”

“…Absorption lines due to highly ionised material have been observed in the spectrum of 4U 1630−47 (Kubota et al 2007;Różańska et al 2014;Díaz Trigo et al 2014;Miller et al 2015).…”

“…Using Suzaku observations carried out in 2006, Kubota et al (2007) studied these absorption line features in relation to the accretiondisc parameters, and concluded that the lines were due to a wind. Using the same Suzaku data, Różańska et al (2014) proposed that the absorption lines could be produced effectively in ⋆ E-mail: yanan@astro.rug.nl the accretion disc atmosphere. Using XMM-Newton observaitons, Díaz Trigo et al (2014) found a thermally/radiatively driven disc wind in 4U 1636−47; the wind becomes more photoionised as the luminosity of the source increases.…”

Chandrahigh-resolution spectra of 4U 1630-47: the disappearance of the wind

“…Thermal pressure consists of the heating of the gas by the central X-ray source, producing an outflow at large distances from the central object, when the thermal velocity is larger than the local escape velocity (Begelman et al 1983;Woods et al 1996;Netzer 2006; Higginbottom E-mail: egatuzzs@eso.org & Proga 2015;Higginbottom et al 2017). Radiative pressure can be produced by electrons scattering, at near-or super-Eddington luminosities, or lines (Różańska et al 2014;Hashizume et al 2015;Shidatsu et al 2016). However, it has been shown that, for BH LMXBs, radiation pressure cannot launch an outflow due to the low number of soft X-ray and UV lines (Proga & Kallman 2002).…”

“…From the observational point of view, thermal winds have been favored by a majority of observations (Kubota et al 2007;Neilsen & Homan 2012;Różańska et al 2014;Díaz Trigo & Boirin 2016;Allen et al 2018;Done et al 2018;Tomaru et al 2018) although radiation pressure due to electrons (Kotani et al 2000;Kubota et al 2007;Neilsen & Lee 2009a;Díaz Trigo et al 2014;Różańska et al 2014;Miller et al 2016b;Shidatsu et al 2016) and magnetic forces (Miller et al 2006a(Miller et al , 2008Luketic et al 2010;King et al 2014;Miller et al 2006aMiller et al , 2016aFukumura et al 2017;Tetarenko et al 2018) have also been invoked to explain a handful of cases.…”