Neutron star masses from hydrodynamical effects in obscured supergiant high mass X-ray binaries

Abstract

Context. A population of obscured supergiant high mass X-ray binaries has been discovered by INTEGRAL. X-ray wind tomography of IGR J17252-3616 inferred a slow wind velocity to account for the enhanced obscuration. Aims. The main goal of this study is to understand under which conditions high obscuration could occur. Methods. We have used an hydrodynamical code to simulate the flow of the stellar wind around the neutron star. A grid of simulations was used to study the dependency of the absorbing column density and of the X-ray light-curves on the model parameters. A comparison between the simulation results and the observations of IGR J17252-3616 provides an estimate on these parameters. Results. We have constrained the wind terminal velocity to 500−600 km s −1 and the neutron star mass to 1.75−2.15 M . Conclusions. We have confirmed that the initial hypothesis of a slow wind velocity with a moderate mass loss rate is valid. The mass of the neutron star can be constrained by studying its impact on the accretion flow.

High-mass X-ray binaries in the Milky Way

“…An important question that is currently under investigation is whether intrinsically clumped winds would survive and have significant additional effect when compared to these of the neutron star. The observability through absorption of the presence of strong tidal streams matching the results of simulations based on CAK winds (Manousakis et al, 2012b) indicate that line driven instability plays a minor role in forming the global structure of the wind close to the surface of the star.…”

“…This suggests that the system is close to Roche lobe overflow (Sidoli et al, 2012). The absence of strong orbital modulation indicates that its transient nature is likely related either to some hydrodynamic properties of the accretion stream (Manousakis et al, 2012b) and/or that a temporary accretion disk might form around the neutron star (see also Ducci et al, 2010, and references therein). The range of luminosity is similar to that observed in Vela X-1.…”

“…-EXO 1722-363: Comparison of observations with hydrodynamic simulations indicate that the large absorbing column density and its variability with orbital phase can be understood if the wind terminal velocity is low and if the neutron star is massive enough (> 1.8 M ⊙ ) to strongly perturb the stellar wind (Manousakis et al, 2012b). -IGR J16320-4751: The absorbing column density is pretty constant at ≈ 10 23 cm −2 (the exact value is model dependent; Rodriguez et al, 2006) along the orbit and increased to 5 × 10 23 cm −2 at one occasion (ZuritaHeras et al, 2009).…”

“…As the neutron stars can cut-off wind acceleration via ionisation (Stevens and Kallman, 1990), the wind can be slower in binaries than in isolated stars. For instance GX 301-2, 4U 1907+09 and EXO 1722-363 feature high absorbing column densities and low wind terminal velocities of 500, 1000 and 600 km/s (Kaper et al, 2006;Kostka and Leahy, 2010;Manousakis et al, 2012b). Even the companion of Vela X-1 has a wind terminal velocity less than what would be expected from its high luminosity (Kudritzki and Puls, 2000).…”

Exploration of spin-down rate of neutron stars in high-mass X-ray binaries

“…Table 2 summarizes the calculated numbers of compact (P orb < 10 days) wind-accreting NS HMXBs in our Galaxy for different models (listed in Table 1). The observed compact (P orb < 10 days) NS HMXBs are listed in Table 3 (Liu, van Paradijs, & van den Heuvel 2006;Wang 2010;Reig et al 2009;Wang & Chang 2012Pearlman, Corbet & Pottschmidt 2013;Manousakis, Walter & Blondin 2012). We find that the spin-down rate in the supersonic propeller phase given by Davies & Pringle (1981) is too low to produce the observed population of compact HMXBs no matter whether the subsonic propeller exists or not.…”