# The bimodality of type Ia Supernovae

## TL;DR

This paper discusses the evidence for bimodal delay times in type Ia supernovae, highlighting two distinct progenitor populations and their observational signatures, and estimates the impact of dust extinction on supernova detection.

## Contribution

It reviews the existing evidence for bimodality in type Ia supernova delay times and estimates the fraction missed due to dust extinction.

## Key findings

- Evidence supports two bimodal delay time distributions.
- Type Ia SNe originate from both young and old progenitors.
- Dust extinction causes some supernovae to be missed in surveys.

## Abstract

We comment on the presence of a bimodality in the distribution of delay time between the formation of the progenitors and their explosion as type Ia SNe. Two "flavors" of such bimodality are present in the literature: a "weak" bimodality, in which type Ia SNe must explode from both young and old progenitors, and a "strong" bimodality, in which about half of the systems explode within 10^8 years from formation. The "weak" bimodality is observationally based on the dependence of the rates with the host galaxy SFR, while the "strong" one on the different rates in radio-loud and radio-quiet early-type galaxies. We review the evidence for these bimodalities. Finally, we estimate the fraction of SNe which are missed by optical and near-IR searches because of dust extinction in massive starbursts.