Progenitors of Type IIb Supernovae: II. Observable Properties

TL;DR

This study uses theoretical models to analyze the properties of Type IIb supernova progenitors, revealing a hidden dominant binary population at low metallicity and emphasizing the importance of unobserved progenitors for understanding supernova mechanisms.

Contribution

It introduces a comprehensive comparison of binary and single progenitor models with observational data, highlighting the existence of an unobserved binary population at low metallicity.

Findings

Binary progenitors can explain observed Type IIb supernovae.

A dominant unobserved population of binary SNe IIb exists at low metallicity.

Highly stripped, compact, blue progenitors are necessary to match supernova fractions.

Abstract

Type IIb supernovae (SNe IIb) present a unique opportunity for investigating the evolutionary channels and mechanisms governing the evolution of stripped-envelope SN progenitors due to a variety of observational constraints available. Comparison of these constraints with the full distribution of theoretical properties not only help ascertain the prevalence of observed properties in nature, but can also reveal currently unobserved populations. In this follow-up paper, we use the large grid of models presented in Sravan et al. 2019 to derive distributions of single and binary SNe IIb progenitor properties and compare them to constraints from three independent observational probes: multi-band SN light-curves, direct progenitor detections, and X-ray/radio observations. Consistent with previous work, we find that while current observations exclude single stars as SN IIb progenitors, SN IIb progenitors in binaries can account for them. We also find that the distributions indicate the existence of an unobserved dominant population of binary SNe IIb at low metallicity that arise due to mass transfer initiated on the Hertzsprung Gap. In particular, our models indicate the existence of a group of highly stripped (envelope mass ~0.1-0.2 M_sun) progenitors that are compact (<50 R_sun) and blue (T_eff <~ 10^5K) with ~10^4.5-10^5.5 L_sun and low density circumstellar mediums. As discussed in Sravan et al. 2019, this group is necessary to account for SN IIb fractions and likely exist regardless of metallicity. The detection of the unobserved populations indicated by our models would support weak stellar winds and inefficient mass transfer in SN IIb progenitors.