Supernova Type Ia progenitors from merging double white dwarfs: Using a new population synthesis model (1208.6446v1)

Abstract: The study of Type Ia supernovae (SNIa) has lead to greatly improved insights into many fields in astrophysics, however a theoretical explanation of the origin of these events is still lacking. We investigate the potential contribution to the SNIa rate from the population of merging double carbon-oxygen white dwarfs. We aim to develope a model that fits the observed SNIa progenitors as well as the observed close double white dwarf population. We differentiate between two scenarios for the common envelope (CE) evolution; the alpha-formalism based on the energy equation and the gamma-formalism that is based on the angular momentum equation. In one model we apply the alpha-formalism always. In the second model the gamma-formalism is applied, unless the binary contains a compact object or the CE is triggered by a tidal instability for which the alpha-formalism is used. The binary population synthesis code SeBa was used to evolve binary systems from the zero-age main sequence to the formation of double white dwarfs and subsequent mergers. SeBa has been thoroughly updated since the last publication of the content of the code. The limited sample of observed double white dwarfs is better represented by the simulated population using the gamma-formalism than the alpha-formalism. For both CE formalisms, we find that although the morphology of the simulated delay time distribution matches that of the observations within the errors, the normalisation and time-integrated rate per stellar mass are a factor 7-12 lower than observed. Furthermore, the characteristics of the simulated populations of merging double carbon-oxygen white dwarfs are discussed and put in the context of alternative SNIa models for merging double white dwarfs.

Supernova Type Ia Progenitors from Merging Double White Dwarfs: Analysis Using a New Population Synthesis Model

Type Ia supernovae (SNIa) stand as critical events in astrophysics, key for understanding cosmology and the chemical enrichment of the universe. Despite their importance, the specific progenitors of SNIa remain the subject of ongoing research and debate. The consensus suggests these supernovae result from thermonuclear explosions of carbon-oxygen (CO) white dwarfs (WDs) with masses near the Chandrasekhar limit. The paper by Toonen et al. explores the hypothesis that merging double white dwarfs (DWDs) could contribute significantly to the supernova Type Ia rates, utilizing a refined population synthesis code named SeBa.

Methodology

The research employs the binary evolution simulation tool SeBa, which has been notably updated for this paper. This code evolves binary systems from the zero-age main sequence to the formation and merger of double white dwarfs. The work distinguishes between two common envelope (CE) evolution scenarios: the α-formalism, which relies on energy conservation, and the γ-formalism, which emphasizes angular momentum. These models influence the subsequent population synthesis of DWDs potentially culminating in SNIa events.

Results

The simulation outcomes provide a calculated delay time distribution (DTD) of potential SNIa progenitors, fitting characteristics observed within available error margins. However, it was found that the normalization and time-integrated SNIa rate per stellar mass are approximately a factor of seven to twelve lower than observational data suggests. Both CE models predict distinct DTD morphologies, yet both exhibit a strong decay indicative of gravitational wave-driven inspirals.

Two significant conclusions emerge regarding supernova progenitors. Firstly, merging DWDs under current models contribute less than previously expected to SNIa rates. Secondly, while observed close DWDs provide a testing ground for model predictions, simulated SNIa progenitor fractional representation is low. Particularly, only a tiny percentage of visible DWDs are thought to be valid SNIa progenitors.

Implications and Future Directions

This paper's findings highlight the intricacy of SNIa progenitor identification, particularly concerning binary evolution pathways leading to DWDs. The mismatch between predicted and observed rates implies additional contributors to the SNIa event rate, possibly from alternative scenarios like the single-degenerate channel or mechanisms involving helium donors.

The implications touch on both theoretical understanding and practical observational strategies. The diverse outcomes from different CE models underscore the unresolved complexities in binary evolution models. The distinct morphologies and rate predictions require refinement and cross-validation with empirical datasets.

Future developments in this research domain should aim at better constraining CE phase parameters, exploring alternative pathways in greater detail, and integrating findings from observational advances in DWD populations. Such efforts will bolster the theoretical framework and foster new insights into the origins of Type Ia supernovae, enhancing their reliability as cosmological tools. Continued synthesis of refined binary evolution codes with observational data will be paramount in achieving a nuanced comprehension of these spectacular cosmic phenomena.