Cen X−3 is a compact high-mass X-ray binary likely powered by Roche lobe overflow. We present a phase-resolved X-ray spectral and timing analysis of two pointed XMM–Newton observations. The first one took place during a normal state of the source, when it has a luminosity LX ∼ 1036 erg s−1. This observation covered orbital phases ϕ = 0.00–0.37, i.e. the egress from the eclipse. The egress light curve is highly structured, showing distinctive intervals. We argue that different intervals correspond to the emergence of different emitting structures. The light-curve analysis enables us to estimate the size of such structures around the compact star, the most conspicuous of which has a size ∼0.3R*, of the order of the Roche lobe radius. During the egress, the equivalent width of Fe emission lines, from highly ionized species, decreases as the X-ray continuum grows. On the other hand, the equivalent width of the Fe K α line, from near-neutral Fe, strengthens. This line is likely formed due to the X-ray illumination of the accretion stream. The second observation was taken when the source was 10 times X-ray brighter and covered the orbital phases ϕ = 0.36–0.80. The X-ray light curve in the high state shows dips. These dips are not caused by absorption but can be due to instabilities in the accretion stream. The typical dip duration, of about 1000 s, is much longer than the time-scale attributed to the accretion of the clumpy stellar wind of the massive donor star, but is similar to the viscous time-scale at the inner radius of the accretion disc.
The aim of this work is to study both light curve and orbital phase spectroscopy of Cen X-3 taking advantage of the MAXI/GSC observation strategy. These studies allow delimiting the stellar wind properties and its interactions with the compact object. From the analysis of the light curve, we have estimated the orbital period of the binary system and also found possible QPOs around a superorbital period of Psuperorb = 220 ± 5 days. Both orbital phase-averaged and phaseresolved spectra were extracted and analysed in the 2.0–20.0 keV energy range. Two models have described spectra satisfactorily, a partial absorbed Comptonization of cool photons on hot electrons plus a power law, and a partial absorbed blackbody plus a power law, both modified by adding Gaussian lines. The high value of the X-ray luminosity in the averaged spectrum indicates that the accretion mode is not only due to the stellar wind.
We present the first XMM-Newton observation of the classical supergiant high-mass X-ray binary XTE J1855−026 taken entirely during the eclipse of the neutron star (NS), covering the orbital phases φ = 0.00–0.11. The analysis of the data allows us to (a) compare with the parameters obtained during the existing pre eclipse observation and (b) explore the back illuminated stellar wind of the B0I type donor. The blackbody component, used to describe the soft excess during pre eclipse, is not observed during eclipse. It must be then produced near the NS or along the donor-NS line. The 0.3–10 keV luminosity during eclipse (∼1034 erg s−1) is 70 times lower than pre eclipse. The intensity of the Fe Kα line, in the average eclipse spectrum, is ∼7.4 times lower than the one measured during pre eclipse. Since Kα photons can not be resonantly scattered in the wind, the vast majority of Fe Kα emission must come from distances within 1R* from the NS. The eclipse spectrum is successfully modelled through the addition of two photoionized plasmas, one with low ionization (log ξ1, cold = 0.36) and high emission measure (EM1, cold ≈ 3 × 1059 cm−3) and another with high ionization (log ξ2, hot = 3.7) and low emission measure (EMhot ≈ 2 × 1056 cm−3). Assuming that the cold and hot gas phases are the clumps and the interclump medium of the stellar wind, respectively, and a clump volume filling factor of ≈[0.04 − 0.05], typical for massive stars, a density contrast between clumps and the interclump medium of nc/ni ≈ 180 is deduced, in agreement with theoretical expectations and optical-UV observations of massive star winds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.