Wind accretion in SGXBs
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Wind accretion in SGXBs
Negueruela
arXiv: 0907.2883v1
Reporter:zhangzhen
09.09.22
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Aim
A review about the possible formation of accretion disks in OB X-ray binary systems
Points: Spin evolution
Wind accretion
Disk formation
Simulation
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Outlines
Introduction: Something about HMXBs
The theory of wind accretion
Analisis about the theoty Real wind Real accretion
Case study GX 301-2 SFXT
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Introduction
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Types of HMXBs Corbet 1986
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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
&
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Modification
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The need for more consideration X-ray light curves (Ribo et al. 2006)
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Spin variation: Vela X-1
(Bildsten et al. 1997)
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Spin variation: 4U 1907+09
(Fritz et al.2006)
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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
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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
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Runacres & Owocki 2004
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Wind structured: overall geometry
Equatorialy enhanced mass loss (Markove et al. 2005; Ud-Doula et al. 2005)
Poles enhanced mass loss (Smith & Townsend 2007)
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Accretion: unstable process Bow shock (Nagae et al. 2005)
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Flip-flop oscillation
2D simulation (Matsuda et al. 1987)
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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
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2D simulation: the smaller the accretor, the more unstable (Blondin & Pope 2009)
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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)
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Magnetid field
Anzer & Borner 1995
Explain Vela X-1 Spin fluctuation
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Case study
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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
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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)
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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
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Sugera et al. 2006
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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
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Summary
Bondi-Hoyle-Lyttleton accretionModification: Clump Flip-flop oscillationExample GX 301-2 SFXT
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Thanks