Detecting the MRI accretion-disc instability in action

Peter [email protected]

Detecting the MRI accretion-disc instability in action

Peter Wheatley

University of Warwick

Movie: James Murray


Magneto-rotational instability (MRI)

Adapted from Balbus & Hawley 1998

Balbus & Hawley 1991


Numerical MRI simulations

• Simulations show MRI can drive angular momentum transport

• But observational handle desirable

Hawley et al.

Miller & Stone 2000


Corona should be phenomenon of the global disc


Observational consequences:

Hot disc corona

Figure: Zdziarski & Gierlinski 2004


Cataclysmic variables

• MRI on/off states in individual systems on accessible timescale

• Eclipses reveal geometry

• Global disc visible


XMM-NewtonWheatley & West 2003

Low state of Z Cha

Optical

X-ray



Low state

low state

Patterson & Raymond 1985


High state

Wheatley, Mauche & Mattei 2003

Optical

EUV

X-ray

SS Cyg


X-ray spectra

low state high state



Naylor et al. 1988

Wheatley & Mauche 2005

Chandra LETGHigh state of WZ Sge

NeVI

NeV OVINeVI

FeVIII


X-ray spectra

low state high state



XMM-NewtonX-ray eclipse

Pratt et al. 2004High state - UX UMa

3-10 keV

0.3-2 keV


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


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





EUVE spectroscopy

OY Car Mauche & Raymond 2000

SS Cyg Mauche, Raymond & Mattei 1995 U Gem Long et al 1996


• Non eclipsing in ob, eg exosat, and others?


EUVE spectroscopy

OY Car Mauche & Raymond 2000

SS Cyg Mauche, Raymond & Mattei 1995 U Gem Long et al 1996



X-ray spectra

quiescence outburst


OY Car with EUVEMauche & Raymond 2000

V~4000 km/sWZ Sge with ChandraNeVI

NeV OVINeVI

FeVIII


X-ray spectra

quiescence outburst


LETG X-ray spectra

kT <= 1 keVNH<<1.4x1021 cm-2

V=840km/sA(Fe)=0.2

kT = 6 keVNH = 1.4x1021cm-2


Peter Wheatley

XMM-Newton and Chandra

observations of dwarf novae


Overview: two topics

• XMM-Newton eclipse observations: OY Car and Z Cha

• Chandra spectroscopy of WZ Sge in superoutburst


X-ray eclipse with ROSATPratt et al 1999

XMM-Newton

Wheatley & West 2003


3 2 14


OY Car eclipse with XMM-NewtonWheatley & West, 2003

1

2 3

4



Magnetic accretion?


Z Cha

ROSAT light curves Van Teeseling,1997


Z ChaWheatley & West, in prep




Overview: two topics

• XMM-Newton eclipse observations, OY Car and Z Cha

• Chandra spectroscopy of WZ Sge in superoutburst


WZ Sge with Chandra

Wheatley & Mauche, in prep.

X-ray

EUV


WZ Sge with Chandra

Wheatley & Mauche, in prep.

X-ray

EUV


outburst orbital hump common superhump

Optical: Patterson et al. 2002

Chandra LETG


X-ray spectra

quiescence outburst



OY Car with EUVEMauche & Raymond 2000

V~4000 km/sWZ Sge with ChandraNeVI

NeV OVINeVI

FeVIII




X-ray spectra

quiescence outburst


LETG X-ray spectra

kT <= 1 keVNH<<1.4x1021 cm-2

V=840km/sA(Fe)=0.2

kT = 6 keVNH = 1.4x1021cm-2


Origin of outburst

soft X-raysFor Against


Origin of outburst


Boundary layerKnown source of X-rays (quiescent eclipses)

• Soft spectrum

• Lack of absorption in WZ Sge in outburst

• UX UMa eclipses


UX UMa eclipse

Pratt et al. 2004

outburst


Origin of outburst



• Soft spectrum


• 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


Origin of outburst



• Soft spectrum


• 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

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Detecting the MRI accretion-disc instability in action