The Nature of the Supersoft X-ray Sources: The Nature of the Supersoft X-ray Sources Katherine McGowan (MSSL) Phil Charles (SAAO), Alex Blustin (MSSL),
Mario Livio (STScI),
Darragh O’Donoghue (SAAO),
Bernard Heathcote (Barfold Observatory)
Supersoft Source Characteristics: Supersoft Source Characteristics Luminous emission at very soft energies
LX ~ 1037 - 1038 erg s-1
< 0.5 keV Greiner et al. 1991
White Dwarf Model: White Dwarf Model Binary system
white dwarf compact object
sub-giant companion
High accretion rate
~ 100 - 1000 higher than in CVs
> 10-7 Msun yr-1
Near-Eddington luminosities achieved as white dwarf burns hydrogen steadily at its surface van den Heuvel et al. 1992
RX J0513.9-6951: RX J0513.9-6951 X-rays detected only during optical low states
Model for X-ray Outbursts: Model for X-ray Outbursts Regular thermonuclear flash model
radius expansion
increase in optical luminosity
Contraction model
accretion rate drops
decrease in optical luminosity
rise in effective temperature
increase in X-ray luminosity Southwell et al. 1996
Optical Monitoring: Optical Monitoring
Multi-wavelength Data: Multi-wavelength Data UV Optical X-ray Hardness ratio (0.5-0.8 keV) (0.3-0.5 keV)
Low-resolution X-ray Spectra: Low-resolution X-ray Spectra Absorption
Spectral Evolution: Spectral Evolution kT LBB RBB LX
High-resolution X-ray Spectra: High-resolution X-ray Spectra
Summary 1: Summary 1 Contraction model based on prediction that rise in X-rays occurs after drop in optical
Detect X-rays in optical low state
X-ray flux and temperature decrease as optical low state progresses
As X-ray outburst evolves peak of emission moves into UV
Radius decreases at start of observations
As optical/UV intensity recover radius increases
Summary 2: Summary 2 Highly ionized gas outflowing at <3000 km/s
Optical depth of ionized absorption increases
Viewing system close to pole-on through bipolar outflow, intrinsic covering factor of outflow changes?
Seeing process of expansion, highly ionized nova by-products stream out from surface and build into optically-thick inflated surface?
increase in optical/UV flux occurs as X-rays are down-scattered in inflated layer?