# The Progenitors of Type Ia Supernovae: Are They Supersoft Sources?

## TL;DR

This paper challenges the idea that most Type Ia supernova progenitors are observable as supersoft X-ray sources, showing that observational data do not support this hypothesis and constraining models of progenitor evolution.

## Contribution

It provides evidence that the majority of progenitors are not observable as supersoft sources, refining the understanding of the evolutionary phases leading to Type Ia supernovae.

## Key findings

- Surveys do not support the hypothesis that many progenitors are observable as SSSs.
- Constraints are placed on sub-Chandrasekhar mass models.
- Progenitors spend only brief phases as SSSs before explosion.

## Abstract

In a canonical model, the progenitors of Type Ia supernovae (SNe Ia) are accreting, nuclear-burning white dwarfs (NBWDs), which explode when the white dwarf reaches the Chandrasekhar mass, M_C. Such massive NBWDs are hot (kT ~100 eV), luminous (L ~ 10^{38} erg/s), and are potentially observable as luminous supersoft X-ray sources (SSSs). During the past several years, surveys for soft X-ray sources in external galaxies have been conducted. This paper shows that the results falsify the hypothesis that a large fraction of progenitors are NBWDs which are presently observable as SSSs. The data also place limits on sub-M_C models. While Type Ia supernova progenitors may pass through one or more phases of SSS activity, these phases are far shorter than the time needed to accrete most of the matter that brings them close to M_C.