Stellar Winds in Massive X-ray Binaries

Monthly Notices of the Royal Astronomical Society

We have carried out radiation-hydrodynamic simulations of thermally-driven accretion disc winds in low-mass X-ray binaries. Our main goal is to study the luminosity dependence of these outflows and compare with observations. The simulations span the range 0.04 ≤ L acc /L Edd ≤ 1.0 and therefore cover most of the parameter space in which disc winds have been observed. Using a detailed Monte Carlo treatment of ionization and radiative transfer, we confirm two key results found in earlier simulations that were carried out in the optically thin limit: (i) the wind velocity -and hence the maximum blueshift seen in wind-formed absorption lines -increases with luminosity; (ii) the large-scale wind geometry is quasi-spherical, but observable absorption features are preferentially produced along high-column equatorial sightlines. In addition, we find that (iii) the wind efficiency always remains approximately constant at Ṁwind / Ṁacc 2, a behaviour that is consistent with observations. We also present synthetic Fe xxv and Fe xxvi absorption line profiles for our simulated disc winds in order to illustrate the observational implications of our results.

2011

K. Postnov ∗a, N. Shakura a, A. González-Galán b, E. Kuulkers c, P. Kretschmar c, S. Larsson d, M.H. Finger e, f , A. Kochetkova a, G. Lüg and L. Yungelson h aSternberg Astronomical Institute, 13, Universitetskij pr ., 119992 Moscow, Russia b Departamento de Física, Ingeniería de Sistemas y Teoría de l S ñal,Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain c European Space Astronomy Centre (ESAC), P.O. Box 78, 28691, Villanueva de la Cañada, Spain d Department of Astronomy, Stockholm University, SE-106 91 S tockholm, Sweden e National Space Science and Technology Center, 320 Sparkman Drive, Huntsville, AL 35805, USA f Universities Space Research Association, 6767 Old Madison Pike, Suite 450, Huntsville, AL 35806, USA g School of Physics, Xinjiang University, Urumqi, 830046 Chi na h Institute of Astronomy RAS, Moscow, 48 Pyatnitskaya Str., M oscow, 119017, Russia E-mail: [email protected], [email protected], [email protected],[email protected] Peter.Kretsc...

The properties of wind accretion in symbiotic X-ray binaries (SyXBs) consisting of red-giant and magnetized neutron star (NS) are discussed. The spin-up/spin-down torques applied to NS are derived based on a hydrodynamic theory of quasi-spherical accretion onto magnetized NSs. In this model, a settling subsonic accretion proceeds through a hot shell formed around the NS magnetosphere. The accretion rate onto the NS is determined by the ability of the plasma to enter the magnetosphere.Due to large Reynolds numbers in the shell, the interaction of the rotating magnetosphere with plasma initiates a subsonic turbulence. The convective motions are capable of carrying the angular momentum through the shell. We carry out a population synthesis of SyXBs in the Galaxy with account for the spin evolution of magnetized NS. The Galactic number of SyXBs with bright (M_v<1) low-mass red-giant companion is found to be from \sim 40 to 120, and their birthrate is \sim 5\times 10^{-5}-10^{-4} per ...

Monthly Notices of the Royal Astronomical Society, 2012

The clumping of massive star winds is an established paradigm confirmed by multiple lines of evidence and supported by stellar wind theory. The purpose of this paper is to bridge the gap between detailed models of inhomogeneous stellar winds in single stars and the phenomenological description of donor winds in supergiant high-mass X-ray binaries (HMXBs). We use results from time-dependent hydrodynamical models of the instability in the line-driven wind of a massive supergiant star to derive the time-dependent accretion rate onto a compact object in the Bondi-Hoyle-Lyttleton approximation. The strong density and velocity fluctuations in the wind result in strong variability of the synthetic X-ray light curves. The model predicts a large scale X-ray variability, up to eight orders of magnitude, on relatively short timescales. The apparent lack of evidence for such strong variability in the observed HMXBs indicates that the details of accretion process act to reduce the variability due to the stellar wind velocity and density jumps.

Monthly Notices of the Royal Astronomical Society

X-ray signatures of outflowing gas have been detected in several accreting black-hole binaries, always in the soft state. A key question raised by these observations is whether these winds might also exist in the hard state. Here, we carry out the first full-frequency radiation hydrodynamic simulations of luminous ($\rm {L = 0.5 \, L_{\mathrm{Edd}}}$) black-hole X-ray binary systems in both the hard and the soft state, with realistic spectral energy distributions (SEDs). Our simulations are designed to describe X-ray transients near the peak of their outburst, just before and after the hard-to-soft state transition. At these luminosities, it is essential to include radiation driving, and we include not only electron scattering, but also photoelectric and line interactions. We find powerful outflows with $\rm {\dot{M}_{wind} \simeq 2 \, \dot{M}_{acc}}$ are driven by thermal and radiation pressure in both hard and soft states. The hard-state wind is significantly faster and carries ap...

Space Science Reviews, 2017

Monthly Notices of the Royal Astronomical Society

We investigate the structure and X-ray emission from the colliding stellar winds in massive star binaries. We find that the opening angle of the contact discontinuity (CD) is overestimated by several formulae in the literature at very small values of the wind momentum ratio, η. We find also that the shocks in the primary (dominant) and secondary winds flare by ≈20 • compared to the CD, and that the entire secondary wind is shocked when η 0.02. Analytical expressions for the opening angles of the shocks, and the fraction of each wind that is shocked, are provided. We find that the X-ray luminosity L x ∝ η, and that the spectrum softens slightly as η decreases.

This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of high-mass X-ray binaries and ultra-luminous X-ray sources. For a summary, we refer to the paper.

2015

X-ray and UV line emission in X-ray binaries can be accounted for by a hot corona. Such a corona forms through irradiation of the outer disk by radiation produced in the inner accretion flow. The same irradiation can produce a strong outflow from the disk at sufficiently large radii. Outflowing gas has been recently detected in several X-ray binaries via blue-shifted absorption lines. However, the causal connection between winds produced by irradiation and the blue-shifted absorption lines is problematic, particularly in the case of GRO J1655-40. Observations of this source imply wind densities about two orders of magnitude higher than theoretically predicted. This discrepancy does not mean that these `thermal disk-winds' cannot explain blue-shifted absorption in other systems, nor that they are unimportant as a sink of matter. Motivated by the inevitability of thermal disk-winds and wealth of data taken with current observatories such as Chandra, XMM-Newton and Suzaku, as well ...

2019

Recent X-ray observations have revealed the complexity and diversity of high-mass X-ray binaries (HMXBs). This diversity challenges a classical understanding of the accretion process onto the compact objects. In this study, we reinforce the conventional concept of the nature of wind-fed accretion onto a neutron star considering the geometrical effect of radiatively accelerated wind, and re-evaluate the transported angular momentum by using a simple wind model. Our results suggest that even in an OB-type HMXB fed by stellar wind, a large amount of angular momentum could be transported to form an accretion disk due to the wind-inhomogeneity, if the binary separation is tight enough and/or stellar wind is slow. We apply our model into actual systems such as LMC X-4 and OAO 1657-415, and discuss the possibility of disk formations in these systems.

X-ray line profiles represent a new way of studying the winds of massive stars. In particular, they enable us to probe in detail the wind-wind collision in colliding wind binaries, providing new insights into the structure and dynamics of the X-ray-emitting regions. We present the key results of new analyses of high-resolution Chandra X-ray spectra of two important colliding wind systems, Gamma Velorum and WR140. The lines of Gamma Vel are essentially unshifted from their rest wavelengths, which we suggest is evidence of a wide shock opening angle, indicative of sudden radiative braking. The widths of the lines of WR140 are correlated with ionization potential, implying non-equilibrium ionization. The implications of these results for the radio emission from these systems are discussed, as are some of the future directions for X-ray line profile modelling of colliding wind binaries.

Astronomy & Astrophysics, 2016

Context. Classical supergiant X-ray binaries (SGXBs) and supergiant fast X-ray transients (SFXTs) are two types of high-mass X-ray binaries (HMXBs) that present similar donors but, at the same time, show very different behavior in the X-rays. The reason for this dichotomy of wind-fed HMXBs is still a matter of debate. Among the several explanations that have been proposed, some of them invoke specific stellar wind properties of the donor stars. Only dedicated empiric analysis of the donors' stellar wind can provide the required information to accomplish an adequate test of these theories. However, such analyses are scarce. Aims. To close this gap, we perform a comparative analysis of the optical companion in two important systems: IGR J17544-2619 (SFXT) and Vela X-1 (SGXB). We analyze the spectra of each star in detail and derive their stellar and wind properties. As a next step, we compare the wind parameters, giving us an excellent chance of recognizing key differences between donor winds in SFXTs and SGXBs. Methods. We use archival infrared, optical and ultraviolet observations, and analyze them with the non-local thermodynamic equilibrium (NLTE) Potsdam Wolf-Rayet model atmosphere code. We derive the physical properties of the stars and their stellar winds, accounting for the influence of X-rays on the stellar winds. Results. We find that the stellar parameters derived from the analysis generally agree well with the spectral types of the two donors: O9I (IGR J17544-2619) and B0.5Iae (Vela X-1). The distance to the sources have been revised and also agree well with the estimations already available in the literature. In IGR J17544-2619 we are able to narrow the uncertainty to d = 3.0 ± 0.2 kpc. From the stellar radius of the donor and its X-ray behavior, the eccentricity of IGR J17544-2619 is constrained to e < 0.25. The derived chemical abundances point to certain mixing during the lifetime of the donors. An important difference between the stellar winds of the two stars is their terminal velocities (∞ = 1500 km s −1 in IGR J17544-2619 and ∞ = 700 km s −1 in Vela X-1), which have important consequences on the X-ray luminosity of these sources. Conclusions. The donors of IGR J17544-2619 and Vela X-1 have similar spectral types as well as similar parameters that physically characterize them and their spectra. In addition, the orbital parameters of the systems are similar too, with a nearly circular orbit and short orbital period. However, they show moderate differences in their stellar wind velocity and the spin period of their neutron star which has a strong impact on the X-ray luminosity of the sources. This specific combination of wind speed and pulsar spin favors an accretion regime with a persistently high luminosity in Vela X-1, while it favors an inhibiting accretion mechanism in IGR J17544-2619. Our study demonstrates that the relative wind velocity is critical in class determination for the HMXBs hosting a supergiant donor, given that it may shift the accretion mechanism from direct accretion to propeller regimes when combined with other parameters.

Astronomy & Astrophysics, 2005

Massive X-ray binaries are usually classified depending on the properties of the donor star in classical, supergiant and Be X-ray binaries. The massive X-ray binary 4U 2206+54 does not fit in any of these groups, and deserves a detailed study to understand how the transfer of matter and the accretion on to the compact object take place. To this end we study an IUE spectrum of the donor and obtain a wind terminal velocity (v_inf) of ~350 km/s, which is abnormally slow for its spectral type. We also analyse here more than 9 years of available RXTE/ASM data. We study the long-term X-ray variability of the source and find it to be similar to that observed in the wind-fed supergiant system Vela X-1, reinforcing the idea that 4U 2206+54 is also a wind-fed system. We find a quasi-period decreasing from ~270 to ~130 d, noticed in previous works but never studied in detail. We discuss possible scenarios and conclude that long-term quasi-periodic variations in the mass-loss rate of the primary are probably driving such variability in the measured X-ray flux. We obtain an improved orbital period of 9.5591 d with maximum X-ray flux at MJD 51856.6. Our study of the orbital X-ray variability in the context of wind accretion suggests a moderate eccentricity around 0.15. Moreover, the low value of v_inf solves the long-standing problem of the relatively high X-ray luminosity for the unevolved nature of the donor, BD +53 2790, which is probably an O9.5 V star. We note that changes in v_inf and/or the mass-loss rate of the primary alone cannot explain the diferent patterns displayed by the orbital X-ray variability. We finally emphasize that 4U 2206+54, together with LS 5039, could be part of a new population of wind-fed HMXBs with main sequence donors, the natural progenitors of supergiant X-ray binaries. (Abridged)

Monthly Notices of the Royal Astronomical Society, 2009

The supersonic stellar and disk winds possessed by massive young stellar objects will produce shocks when they collide against the interior of a pre-existing bipolar cavity (resulting from an earlier phase of jet activity). The shock heated gas emits thermal X-rays which may be observable by spaceborne observatories such as the Chandra X-ray Observatory. Hydrodynamical models are used to explore the wind-cavity interaction. Radiative transfer calculations are performed on the simulation output to produce synthetic X-ray observations, allowing constraints to be placed on model parameters through comparisons with observations. The model reveals an intricate interplay between the inflowing and outflowing material and is successful in reproducing the observed X-ray count rates from massive young stellar objects.

arXiv (Cornell University), 2022

Ultraluminous X-ray sources (ULXs) are extreme X-ray binaries shining above 10 39 erg/s, in most cases as a consequence of super-Eddington accretion onto neutron stars and stellar-mass black holes accreting above their Eddington limit. This was understood after the discovery of coherent pulsations, cyclotron lines and powerful winds. The latter was possible thanks to the high-resolution X-ray spectrometers aboard XMM-Newton. ULX winds carry a huge amount of power owing to their relativistic speeds (0.1-0.3) and are able to significantly affect the surrounding medium, likely producing the observed 100 pc ULX superbubbles, and limit the amount of matter that can reach the central accretor. The study of ULX winds is therefore quintessential to understand 1) how much and how fast can matter be accreted by compact objects and 2) how strong is their feedback onto the surrounding medium. This is also relevant to understand supermassive black holes growth. Here we provide an overview on this phenomenology, highlight some recent, exciting results and show how future missions such as XRISM, eXTP and ATHENA will improve our understanding.