Origin of Ne Emission Line of Very Luminous Soft X-ray Transient MAXI J0158$-$744

Abstract

We investigate the mechanism to reproduce notable spectral features at the ignition phase of nova explosion observed for a super-Eddington X-ray transient source MAXI J0158$-$744 in the Small Magellanic Cloud. These are a strong Ne IX emission line at 0.92 keV with a large equivalent width of $0.32_{-0.11}^{+0.21}$ keV and the absence of Ne X line at 1.02 keV. In this paper, we calculate the radiative transfer using a Monte Carlo code, taking into account the line blanketing effect due to transitions of N, O, Ne, Mg and Al ions in an accelerating wind emanating from a white dwarf with a structure based on a spherically symmetric stationary model. We found that the strong Ne IX line can be reproduced if the mass fraction of Ne is enhanced to $10^{-3}$ or more and that of O is reduced to $\sim 5\times 10^{-9}$ or less and that the absence of other lines including Ne X ions at higher energies can be also reproduced by the line blanketing effect. This enhancement of the Ne mass fraction indicates that the ejecta are enriched by Ne dredged up from the surface of the white dwarf composed of O, Ne, and Mg rather than C and O, as already pointed out in the previous work. We argue that the CNO cycle driving this nova explosion converted most of C and O into N and thus reduced the O mass fraction.

arXiv comment7 pages, 9 figures, accepted for publication in ApJ

References in corpus (9)

• The MAXI Mission on the ISS: Science and Instruments for Monitoring All Sky X-Ray Images
• Gas Slit Camera (GSC) onboard MAXI on ISS
• Swift X-Ray Observations of Classical Novae. II. The Super Soft Source sample
• The Chemical Enrichment History of the Small Magellanic Cloud and Its Gradients
• In-Orbit Performance of MAXI Gas Slit Camera (GSC) on ISS
• Solid-state Slit Camera (SSC) on Board MAXI
• In Orbit Performance of the MAXI/SSC onboard the ISS
• A Luminous Be+White Dwarf Supersoft Source in the Wing of the SMC: MAXI J0158-744
• Extraordinary luminous soft X-ray transient MAXI J0158-744 as an ignition of a nova on a very massive O-Ne white dwarf

Cited by in corpus (3)

• OGLE Atlas of Classical Novae. II. Magellanic Clouds
• Search for Soft X-ray Flashes at Fireball Phase of Classical/Recurrent Novae using MAXI/GSC data
• The optically thick rotating magnetic wind from a massive white dwarf merger product