EDP Sciences
Free access
Volume 476, Number 1, December II 2007
Page(s) 335 - 340
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20078353

A&A 476, 335-340 (2007)
DOI: 10.1051/0004-6361:20078353

Probing clumpy stellar winds with a neutron star

R. Walter1, 2 and J. Zurita Heras3

1  INTEGRAL Science Data Centre, Chemin d'Ecogia 16, 1290 Versoix, Switzerland
    e-mail: Roland.Walter@obs.unige.ch
2  Observatoire de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
3  Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette, France
    e-mail: juan-antonio.zurita-heras@cea.fr

(Received 25 July 2007 / Accepted 8 October 2007 )

Context.INTEGRAL, the European Space Agency's $\gamma$-ray observatory, tripled the number of super-giant high-mass X-ray binaries (sgHMXB) known in the Galaxy by revealing absorbed and fast transient (SFXT) systems.
Aims.In these sources, quantitative constraints on the wind clumping of the massive stars could be obtained from the study of the hard X-ray variability of the compact accreting object.
Methods.Hard X-ray flares and quiescent emission of SFXT systems have been characterized and used to derive wind clump parameters.
Results.A large fraction of the hard X-ray emission is emitted in the form of flares with a typical duration of 3 ks, frequency of 7 days and luminosity of 1036 erg/s. Such flares are most probably emitted by the interaction of a compact object orbiting at ~10 $R_{\ast}$ with wind clumps ( 1022-23 g) representing a large fraction of the stellar mass-loss rate. The density ratio between the clumps and the inter-clump medium is 102-4 in SFXT systems.
Conclusions.The parameters of the clumps and of the inter-clump medium, derived from the SFXT flaring behavior, are in good agreement with macro-clumping scenario and line driven instability simulations. SFXT have probably a larger orbital radius than classical sgHMXB.

Key words: gamma rays: observations -- X-rays: binaries -- pulsars: general -- stars: winds, outflows -- supergiants

© ESO 2007