1. Wind accretion in SGXBs Negueruela arXiv: 0907.2883v1 Reporter:zhangzhen 09.09.22

2. Aim • A review about the possible formation of accretion disks in OB X-ray binary systems • Points: Spin evolution Wind accretion Disk formation Simulation

3. Outlines • Introduction: Something about HMXBs The theory of wind accretion • Analisis about the theoty Real wind Real accretion • Case study GX 301-2 SFXT

4. Introduction

5. Types of HMXBs • Corbet 1986

6. The theory of wind accretion • Bondi-Hoyle-Lyttleton accretion the supersonic motion of a point mass through a gas cloud then

7. Modification

8. The need for more consideration • X-ray light curves (Ribo et al. 2006)

9. Spin variation: Vela X-1 (Bildsten et al. 1997)

10. Spin variation: 4U 1907+09 (Fritz et al.2006)

11. Aspects of modification • The wind of massive stars are highly structured • Accretion on to a very small object is an unstable process • The magnetic field of the neutron star may affect the flow of material

12. Wind structured: clump • Observation: large-scale cyclical structures (Kaper & Fullerton 1998 Springer) • Simulations (runacres & Osocki 2002) • OB star spectra (Prinja et al. 2005) • H profile of O-type star (Markova et al. 2005) • No direct obsevational evidences • Not smooth, constant density

13. Runacres & Owocki 2004

14. Wind structured: overall geometry • Equatorialy enhanced mass loss (Markove et al. 2005; Ud-Doula et al. 2005) • Poles enhanced mass loss (Smith & Townsend 2007)

15. Accretion: unstable process • Bow shock (Nagae et al. 2005)

16. Flip-flop oscillation 2D simulation (Matsuda et al. 1987)

18. Flip-flop oscillation 3D simulation: stable flow (Ruffert et al. 1999; Kryukov et al. 2005) flip-flop oscillation ---- a numerical artifact a review: Foglizzo et al. 2005 flip-flop instability ---- physical origin the coupling of advected perturbation to acoustic waves

19. 2D simulation: the smaller the accretor, the more unstable (Blondin & Pope 2009)

20. Photo-ionisation • Emitting X-ray  ionising the heavy elements  slowing down the wind  increasing the accretion radius (Blondin et al. 1991) • Wind lines orbital variability (Kaper et al. 1993) • Far ultra violet spectra of the counterpart to 4U 1700-37 (Iping et al.2007)

21. Magnetid field • Anzer & Borner 1995 • Explain Vela X-1 • Spin fluctuation

22. Case study

23. GX 301-2 • Feature: Wide: Porb=41.5d Eccentric: e=0.45 Companion: B1 Ia+ hypergiant Denser, slower wind Flux: ~4 times higher close to periastron Peaking 1-2d before periastron

24. Explanation for GX 301-2 • The size of the hypergiant may be very close to filling its Roche lobe at periastron allowing the formation of an accretion stream (Koh et al. 1997) • The existence of such a stream in optical spectra of the companion (Kaper et al. 2006) • The average X-ray lightcurve can be fit by accretion from a spherical wind and an accretion disk (Leahy & Kostka 2008)

25. Supergiant fast X-ray transients • Brief outbursts with a rise timescale of tens of minutes and lasting only a few hours • OB supergiants • Lx 10^36erg/s at the peak of the outbursts Lx 10^33~10^35erg/s outside the outbursts • Spectra and lightcurves: wind accretion

26. Sugera et al. 2006

27. Explanation for SFXT • Clumps: In’t Zand (2005) Walter & Zurita Heras (2007) • Thin circumstellar disk surrounding the supergiant (Sidoli et al. 2007) • Interaction of the wind and the magnetosphere (Grebenev & sunyaev 2007) • Kreykenbohm et al. 2008

28. Summary • Bondi-Hoyle-Lyttleton accretion • Modification: Clump Flip-flop oscillation • Example GX 301-2 SFXT

29. Thanks