The Progenitors of Type Ia Supernovae: II. Are they Double-Degenerate Binaries? The Symbiotic Channel

TL;DR

This paper investigates the progenitor systems of Type Ia supernovae, focusing on the role of double-degenerate binaries and symbiotic channels, and challenges previous assumptions about their detectability as supersoft X-ray sources.

Contribution

It demonstrates that many potential progenitors pass through a long-lived nuclear-burning white dwarf phase, which can be detectable as symbiotic binaries, thus addressing the progenitor problem.

Findings

Many pre-double-degenerate systems are likely to be observable as symbiotic binaries.

The scarcity of supersoft X-ray sources does not rule out double-degenerate progenitors.

Most nuclear-burning white dwarfs do not appear as supersoft sources most of the time.

Abstract

In order for a white dwarf (WD) to achieve the Chandrasekhar mass, M_C, and explode as a Type Ia supernova (SNIa), it must interact with another star, either accreting matter from or merging with it. The failure to identify the types of binaries which produce SNeIa is the "progenitor problem". Its solution is required if we are to utilize the full potential of SNeIa to elucidate basic cosmological and physical principles. In single-degenerate models, a WD accretes and burns matter at high rates. Nuclear-burning WDs (NBWDs) with mass close to M_C are hot and luminous, potentially detectable as supersoft x-ray sources (SSSs). In previous work we showed that > 90-99% of the required number of progenitors do not appear as SSSs during most of the crucial phase of mass increase. The obvious implication is that double-degenerate (DD) binaries form the main class of progenitors. We show in this paper, however, that many binaries that later become DDs must pass through a long-lived NBWD phase during which they are potentially detectable as SSSs. The paucity of SSSs is therefore not a strong argument in favor of DD models. Those NBWDs that are the progenitors of DD binaries are likely to appear as symbiotic binaries for intervals > 10^6 years. In fact, symbiotic pre-DDs should be common, whether or not the WDs eventually produce SNeIa. The key to solving the progenitor problem lies in understanding the appearance of NBWDs. Most do not appear as SSSs most of the time. We therefore consider the evolution of NBWDs to address the question of what their appearance may be and how we can hope to detect them.