ASASSN-16oh: A nova outburst with no mass ejection -- A new type of supersoft X-ray source in old populations

Abstract

ASASSN-16oh is a peculiar transient supersoft X-ray source without a mass-ejection signature in the field of the Small Magellanic Cloud. Maccarone et al. (2019) concluded that ASASSN-16oh is the first dwarf nova with supersoft X-ray that originated from an equatorial accretion belt on a white dwarf (WD). Hillman et al. (2019) proposed a thermonuclear runaway model that both the X-rays and $V$/$I$ photons are emitted from the hot WD. We calculated the same parameter models as Hillman et al.'s and found that they manipulated on/off the mass-accretion, and their best fit $V$ light curves are 6 mag fainter, and decay about 10 times slower, than that of ASASSN-16oh. We propose a nova model induced by a high rate of mass accretion during a dwarf nova outburst, i.e., the X-rays originate from the surface of the hydrogen-burning WD whereas the $V/I$ photons are from the irradiated disk. Our model explains the main observational properties of ASASSN-16oh. We also obtained thermonuclear runaway models with no mass ejection for a wide range of parameters of the WD mass and mass accretion rates including both natural and forced novae in low-metal environments of $Z=0.001$ and $Z=0.0001$. They are a new type of periodic supersoft X-ray sources with no mass ejection, and also a bright transient in $V$/$I$ bands if they have a large disk. We suggest that such objects are candidates of Type Ia supernova progenitors because its mass is increasing at a very high efficiency $(\sim 100\%)$.

references updated, 21 pages, 10 figures, published in ApJ, 892, 15 (2020)

References in corpus (10)

• An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent
• A Universal Decline Law of Classical Novae
• Supersoft X-ray Light Curve of RS Ophiuchi (2006)
• Shortest Recurrence Periods of Novae
• Observational Signatures of SNIa Progenitors, as Predicted by Models
• A Light Curve Analysis of Classical Novae: Free-free Emission vs. Photospheric Emission
• A Light Curve Analysis of 32 Recent Galactic Novae --- Distances and White Dwarf Masses
• Multiplicity of Nova Envelope Solutions and Occurrence of Optically Thick Winds
• The supersoft X-ray transient ASASSN-16oh as a thermonuclear runaway without mass ejection
• The $UBV$ Color Evolution of Classical Novae. III. Time-Stretched Color-Magnitude Diagram of Novae in Outburst

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• Theoretical light curve models of the symbiotic nova CN Cha -- Optical flat peak for three years
• Millinovae: A New Class of Transient Supersoft X-ray Sources without a Classical Nova Eruption
• A light curve model of V2491 Cyg: Classical nova outburst on a cool and massive white dwarf