Footprints in the wind of Vela X-1 traced with MAXI

Abstract

The stellar wind around the compact object in luminous wind-accreting high mass X-ray binaries is expected to be strongly ionized with the X-rays coming from the compact object. The stellar wind of hot stars is mostly driven by light absorption in lines of heavier elements, and X-ray photo-ionization significantly reduces the radiative force within the so-called Stroemgren region leading to wind stagnation around the compact object. In close binaries like Vela X-1 this effect might alter the wind structure throughout the system. Using the spectral data from Monitor of All-sky X-ray Image (MAXI), we study the observed dependence of the photoelectric absorption as function of orbital phase in Vela X-1, and find that it is inconsistent with expectations for a spherically-symmetric smooth wind. Taking into account previous investigations we develop a simple model for wind structure with a stream-like photoionization wake region of slower and denser wind trailing the neutron star responsible for the observed absorption curve.

5 pages, 3 figures, accepted in A&A

References in corpus (8)

• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates
• Gas Slit Camera (GSC) onboard MAXI on ISS
• X-ray Spectral Study of the Photoionized Stellar Wind in Vela~X-1
• High variability in Vela X-1: giant flares and off states
• Witnessing the magnetospheric boundary at work in Vela X-1
• Neutron star masses from hydrodynamical effects in obscured sgHMXBs
• X-ray photoionized bubble in the wind of Vela X-1 pulsar supergiant companion
• A Spectral Study of the Black Hole Candidate XTE J1752-223 in the High/Soft State with MAXI, Suzaku and Swift

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