Volume 554, June 2013
|Number of page(s)||5|
|Published online||31 May 2013|
Footprints in the wind of Vela X–1 traced with MAXI⋆
1 Institut für Astronomie und Astrophysik, Sand 1, 72076 Tübingen, Germany
2 MAXI team, RIKEN, 2-1 Hirosawa, Wako, 351-0198 Saitama, Japan
3 School of Dentistry at Matsudo, Nihon University, 2-870-1, Sakaecho-nishi, Matsudo, 271-8587 Chiba, Japan
4 ISS Science Project Office, Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), 2-1-1 Sengen, Tsukuba, 305-8505 Ibaraki, Japan
5 Department of Physics, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku, 113-0033 Tokyo, Japan
Received: 16 February 2013
Accepted: 21 April 2013
The stellar wind around a 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 Strömgren 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 the Monitor of All-sky X-ray Image (MAXI), we studied the observed dependence of the photoelectric absorption as a function of the orbital phase in Vela X−1 and found that it is inconsistent with expectations for a spherically symmetric smooth wind. Taking into account previous investigations, we developed a simple model for wind structure with a stream-like photoionization wake region of slower and denser wind trailing the neutron star, which is responsible for the observed absorption curve.
Key words: binaries: eclipsing / X-rays: binaries / pulsars: individual: Vela X-1
The movie associated to Fig. 3 is available in electronic form at http://www.aanda.org
© ESO, 2013
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