Origin of outburst X-ray emission

Peter Wheatley, University of Warwick

Dwarf nova X-ray emission

Wheatley, Mauche & Mattei 2003

Optical

EUV

X-ray

outburstquiescence

Patterson & Raymond 1985

X-ray eclipse in quiescence

Mukai et al., 1997HT Cas with ASCA

Z Cha in quiescence with XMM-NewtonHickman et al., in prep

B band

0.2-12 keV

WD eclipse

Z Cha optical eclipse Hickman et al., in prep

B band

1.2-10 keV

0.2-1.2 keV

Hickman et al., in prepZ Cha X-ray eclipse

X-ray spectra

quiescence outburst

Patterson & Raymond 1985

Confirmed

Reis et al., in prep

1029 erg s-1 ~ 1012 g s-1 ~ 10-14 MSun yr-1

X-ray luminosities of white-dwarf dominated CVs

Reis et al., in prep

X-ray spectra

quiescence outburst

Patterson & Raymond 1985

Confirmed

Naylor et al. 1988

OY Car in outburst with EXOSAT LE

7-250 Å

EUV spectra of dwarf novae in outburst

Mauche 2004

WZ Sgehigh inclination

SS Cyglow inclination

Lbl~1034 erg s-1 NH~3x1019 cm-2 V~2500 km s-1

X-ray spectra

quiescence outburst

Patterson & Raymond 1985

Confirmed Confirmed?

NH~3x1019 cm-2

OY Car in outburst with ROSAT - no X-ray eclipse

Pratt et al., 1999

Z Cha in outburst with XMM-Newton

outburst

quiescence

XMM-Newton spectra of Z Cha

outburst

quiescence

X-ray scattering?

UX UMa with XMM-Newton

Pratt et al., 2004

• Nova-like used as proxy for outburst state

Not X-ray scattering

Wheatley & Kallman 2006

UX UMa Pratt et al., 2004

NH=5x1020 cm-2

Nature of outburst X-ray emission

• Properties– Spectrum is unabsorbed optically-thin thermal emission

• weighted to low temperatures compared with quiescence

– Not eclipsed– Not scattered– Only present in outburst– Lx ~ 1031 erg s-1 ~ 10-3 Ldisc

• Origin– Boundary layer - No

• Not eclipsed, not scattered

– Secondary star - No• Too luminous, turns off in quiescence

– Disc hotspot - No• Not eclipsed, turns off in quiescence

– Accretion disc corona - Maybe– Shocks in radiatively-driven wind - Maybe

WZ Sge with Chandra LETG

Wheatley & Mauche 2005

Outburst

Outburst

Quiescence

kT <= 1 keV

v=840 km/s

RKep~2x1010cm

Lx ~ 1031 erg s-1 ~ 10-3 Ldisc

Lx <= 10-3 Lstar

Z Cha in outburst with XMM-Newton

outburst

quiescence

Conclusions

• Eclipses confirm that all quiescent X-ray emission from BL– Useful for estimating instantaneous accretion rates

• Outburst EUV spectra and lack of EUV eclipse consistent with BL dominating outburst emission as well

• However, outburst X-ray spectra and lack of X-ray eclipses are NOT consistent with origin in BL

• Properties of outburst X-ray emission only consistent with a disc corona– Disc corona only only in outburst points to magneto-rotational instability

– Outburst X-rays may provide the best observational handle on the MRI

Magneto-rotational instability (MRI)

Adapted from Balbus & Hawley 1998

Balbus & Hawley 1991