Wind accretion in SGXBs

Negueruela

arXiv: 0907.2883v1

Reporter:zhangzhen

09.09.22

Aim

A review about the possible formation of accretion disks in OB X-ray binary systems

Points: Spin evolution

Wind accretion

Disk formation

Simulation

Outlines

Introduction: Something about HMXBs

The theory of wind accretion

Analisis about the theoty Real wind Real accretion

Case study GX 301-2 SFXT

Introduction

Types of HMXBs Corbet 1986

The theory of wind accretion

Bondi-Hoyle-Lyttleton accretion

the supersonic motion of a point mass through a gas cloud

then

2 * *2

21

2 relrel

GM GMv r

r v: :

2 2* 2

( ) ( )/ 4( ) w

wrel

v r rM V t r v GM

v

&

Modification

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

Spin variation: Vela X-1

(Bildsten et al. 1997)

Spin variation: 4U 1907+09

(Fritz et al.2006)

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

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

Runacres & Owocki 2004

Wind structured: overall geometry

Equatorialy enhanced mass loss (Markove et al. 2005; Ud-Doula et al. 2005)

Poles enhanced mass loss (Smith & Townsend 2007)

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

Flip-flop oscillation

2D simulation (Matsuda et al. 1987)

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

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

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)

Magnetid field

Anzer & Borner 1995

Explain Vela X-1 Spin fluctuation

Case study

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

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)

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

Sugera et al. 2006

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

Summary

Bondi-Hoyle-Lyttleton accretionModification: Clump Flip-flop oscillationExample GX 301-2 SFXT

Thanks