H. Li et al- Rossby Wave Instability of Thin Accretion Disks – III. Nonlinear Simulations
Detecting the MRI accretion-disc instability in action
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Transcript of Detecting the MRI accretion-disc instability in action
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Detecting the MRI accretion-disc instability in action
Peter Wheatley
University of Warwick
Movie: James Murray
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Magneto-rotational instability (MRI)
Adapted from Balbus & Hawley 1998
Balbus & Hawley 1991
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Numerical MRI simulations
• Simulations show MRI can drive angular momentum transport
• But observational handle desirable
Hawley et al.
Miller & Stone 2000
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Corona should be phenomenon of the global disc
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Observational consequences:
Hot disc corona
Figure: Zdziarski & Gierlinski 2004
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Cataclysmic variables
• MRI on/off states in individual systems on accessible timescale
• Eclipses reveal geometry
• Global disc visible
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Naylor et al. 1988
Wheatley & Mauche 2005
Chandra LETGHigh state of WZ Sge
NeVI
NeV OVINeVI
FeVIII
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XMM-NewtonX-ray eclipse
Pratt et al. 2004High state - UX UMa
3-10 keV
0.3-2 keV
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Chandra LETG
Wheatley & Mauche 2005
high state
high state
low state
kT <= 1 keV
v=840km/s
RKep~2x1010cm
Disappears in low state
WZ Sge
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Conclusions
• Probable detection of MRI-driven X-ray corona in CVs
• Evidence includes:1. Extended emission (eclipses)
2. Accretion disc dynamics (line widths)
3. Coronal temperatures (line ratios)
4. Absent in low state
• Excellent potential to follow MRI in action
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EUVE spectroscopy
OY Car Mauche & Raymond 2000
SS Cyg Mauche, Raymond & Mattei 1995 U Gem Long et al 1996
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• Non eclipsing in ob, eg exosat, and others?
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EUVE spectroscopy
OY Car Mauche & Raymond 2000
SS Cyg Mauche, Raymond & Mattei 1995 U Gem Long et al 1996
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OY Car with EUVEMauche & Raymond 2000
V~4000 km/sWZ Sge with ChandraNeVI
NeV OVINeVI
FeVIII
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LETG X-ray spectra
kT <= 1 keVNH<<1.4x1021 cm-2
V=840km/sA(Fe)=0.2
kT = 6 keVNH = 1.4x1021cm-2
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Overview: two topics
• XMM-Newton eclipse observations: OY Car and Z Cha
• Chandra spectroscopy of WZ Sge in superoutburst
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3 2 14
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Magnetic accretion?
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Z ChaWheatley & West, in prep
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Overview: two topics
• XMM-Newton eclipse observations, OY Car and Z Cha
• Chandra spectroscopy of WZ Sge in superoutburst
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outburst orbital hump common superhump
Optical: Patterson et al. 2002
Chandra LETG
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OY Car with EUVEMauche & Raymond 2000
V~4000 km/sWZ Sge with ChandraNeVI
NeV OVINeVI
FeVIII
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LETG X-ray spectra
kT <= 1 keVNH<<1.4x1021 cm-2
V=840km/sA(Fe)=0.2
kT = 6 keVNH = 1.4x1021cm-2
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Origin of outburst
soft X-raysFor Against
Boundary layerKnown source of X-rays (quiescent eclipses)
• Soft spectrum
• Lack of absorption in WZ Sge in outburst
• UX UMa eclipses
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Origin of outburst
soft X-raysFor Against
Boundary layerKnown source of X-rays (quiescent eclipses)
• Soft spectrum
• Lack of absorption in WZ Sge in outburst
• UX UMa eclipses
Scattering in windKnown source of EUV: OY Car & WZ Sge
• Lack of strong continuum to scatter
• High-excitiation lines
• Width of emission lines
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Origin of outburst
soft X-raysFor Against
Boundary layerKnown source of X-rays (quiescent eclipses)
• Soft spectrum
• Lack of absorption in WZ Sge in outburst
• UX UMa eclipses
Scattering in windKnown source of EUV: OY Car & WZ Sge
• Lack of strong continuum to scatter
• High-excitiation lines
• Width of emission lines
Accretion disc
coronal emission
Explains:
• Soft spectrum
• Lack of abso in WZ Sge
• UX UMa eclipse
• Width of lines: RKep~2x1010cm
?