Accreting White Dwarfs as Supersoft X-ray Sources

Abstract

I review various phenomena associated with mass-accreting white dwarfs (WDs) in the view of supersoft X-ray sources. When the mass-accretion rate is low (\dot M_{acc} < a few \times 10^{-7} M_\sun yr^{-1}), hydrogen nuclear burning is unstable and nova outbursts occur. A nova is a transient supersoft X-ray source (SSS) in its later phase which timescale depends strongly on the WD mass. The X-ray turn on/off time is a good indicator of the WD mass. At an intermediate mass-accretion rate an accreting WD becomes a persistent SSS with steady hydrogen burning. For a higher mass-accretion rate, the WD undergoes "accretion wind evolution" in which the WD accretes matter from the equatorial plane and loses mass by optically thick winds from the other directions. Two SSS, namely RX J 0513-69 and V Sge, are corresponding objects to this accretion wind evolution. We can specify mass increasing WDs from light-curve analysis based on the optically thick wind theory using multiwavelength observational data including optical, IR, and supersoft X-rays. Mass estimates of individual objects give important information for the binary evolution scenario of type Ia supernovae.

6 pages including 10 figures, conference proceedings of "Supersoft X-ray Sources - New Developments" (18th - 20th May 2009, European Space Astronomy Centre (ESAC), Villafranca del Castillo, Madrid, Spain)

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• The first nova eruption in a novalike variable: YZ Ret as seen in X-rays and gamma-rays
• Multiwavelength modelling the SED of supersoft X-ray sources. I. The method and examples
• Optical and X-ray Properties of CAL 83: I. Quasi-periodic Optical and Supersoft Variability
• A Light-Curve Model of the Symbiotic Nova PU Vul (1979) -- A Very Quiet Explosion with Long-Lasted Flat Peak
• The confirmation and revision on the orbital period change of the possible type Ia supernova progenitor V617 Sagittarii
• Transient X-ray Sources in the Magellanic-type Galaxy NGC 4449