Clumpy wind accretion in Supergiant X-ray binaries
Abstract
Supergiant X-ray Binaries (SgXB) host a neutron star (NS) accreting a fraction of the intense wind from an evolved O/B Supergiant companion. The X-ray emission associated to accretion displays photometric and spectroscopic variability in time which has partly been attributed to overdensities (aka clumps) in the stellar wind. Recently, the micro-structure of the wind mass and dimension of these clumps. To evaluate the impact of the serendipitous a has been computed by Sundqvist et al (2017), shedding new light the on the mass and dimension of these clumps. To evaluate the impact of their serendipitous accretion on the time variability of the mass accretion rates, we plunge the NS into the wind and performed 3D simulations of the accretion process. We follow the inhomogeneous flow over several orders of magnitude, from the hydrodynamical bow shock down to the NS magnetosphere, and identify the conditions favorable to the formation of a transient disc-like structure within the shocked region. We also account for the variable absorption due to unaccreted clumps passing by the line-of-sight and estimate the final effective variability of the mass accretion rate for different orbital separations. By confronting our results to observations of Vela X-1 by Grinberg et al (2017), we conclude that, if the variability at low luminosity is essentially due to clumps, they can not explain, per se, the flaring activity which must find its origin within the NS magnetosphere.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E.973E