Accretion in supergiant High Mass X-ray Binaries

Antonios Manousakis,John Blondin,Roland Walter,E Bozzo,P Kretschmar,C Ferrigno,M Audard,M Falanga

doi:10.1051/epjconf/20136402006

Abstract

Supergiant High Mass X-ray Binary systems (sgHMXBs) consist of a massive, late type, star and a neutron star. The massive stars exhibits strong, radiatively driven, stellar winds. Wind accretion onto compact object triggers X-ray emission, which alters the stellar wind significantly. Hydrodynamic simulation has been used to study the neutron star - stellar wind interaction it two sgHMXBs: i) A heavily obscured sgHMXB (IGR J17252-3616) discovered by INTEGRAL. To account for observable quantities (i.e., absorbing column density) we have to assume a very slow wind terminal velocity of about 500 km/s and a rather massive neutron star. If confirmed in other obscured systems, this could provide a completely new stellar wind diagnostics. ii) A classical sgHMXB (Vela X-1) has been studied in depth to understand the origin of the off-states observed in this system. Among many models used to account for this observed behavior (clumpy wind, gating mechanism) we propose that self-organized criticality of the accretion stream is the likely reason for the observed behavior. In conclusion, the neutron star, in these two examples, acts very efficiently as a probe to study stellar winds.

Highlights

In supergiant High Mass X-ray Binaries neutron stars are orbiting at a close distance of α ∼ 1.5 − 2 R∗ from their companion stars
The interactions between the neutron star and the stellar wind in Vela X-1 revealed that the wind of the massive star is heavily disrupted by the gravity and photoionization of the neutron star [2, 3]
The code produces density and ionization (ξ = LX/nrn2s, where LX is the average X-ray luminosity, n is the number density at the distance rns from the neutron star [6]) maps that are stored

Summary

Introduction

In supergiant High Mass X-ray Binaries (sgHMXBs) neutron stars are orbiting at a close distance of α ∼ 1.5 − 2 R∗ from their companion stars. The heavily obscured sgHMXBs share some of the characteristics of the classical sgHMXBs. The main difference between classical and obscured sgHMXBs is that the latter ones are much more absorbed in the X-rays (NH > 1023 cm−2) on average, 10 times larger than in classical systems and well above the galactic absorption. The main difference between classical and obscured sgHMXBs is that the latter ones are much more absorbed in the X-rays (NH > 1023 cm−2) on average, 10 times larger than in classical systems and well above the galactic absorption

The simulations

Obscured sgHMXB

Conclusion