A Comprehensive Investigation of Type IIb Supernova Progenitors: Combining Theory, Observations, and Statistics

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{\\it Context}: Type IIb supernovae (SNe) are important candidates to understand mechanisms that drive the stripping of stripped-envelope (SE) supernova (SN) progenitors. ', 'While binary interactions and their high incidence are generally cited to favor them as Type IIb SN progenitors, this idea has not been tested using models covering a broad parameter space.', '{\\it Aims}: In this work we use single- and binary-star models at solar and low metallicities covering a broad parameter space to investigate the progenitors of and evolutionary pathways to Type IIb SNe. ', 'We also estimate theoretical Type IIb SN rates and make predictions for observable constraints.', 'We also perform a case study on SN 2016gkg using Bayesian inference to derive the probability distributions of its progenitors using existing observational constraints.', '{\\it Methods}: We use the largest database of self-consistently computed Type IIb progenitor models, statistical inference methods and multiple comparison methods to observations. As a result, our work provides the strongest constraints on Type IIb progenitors and progenitor channels to date. ', '{\\it Results}: We find that the parameter space for single-star SN IIb progenitors decreases and that for binary-star SN IIb progenitors increases with decreasing metallicity. ', 'We find that single and binary stars contribute roughly the same as Type IIb SNe at solar metallicity. ', 'Binary stars only dominate as progenitors at low metallicity. ', 'We also find that our models can account for less than half the observationally inferred rate for Type IIb SNe at high metallicity, making up $<4.5$\\% of all core-collapse (CC) SNe. ', 'On the other hand, our models can account for the rates currently indicated by observations at low metallicity, making up $0.5-15$\\% of all CC SNe. ', 'However, this requires low mass transfer efficiencies ($\\sim 0.1$) in the binaries. ', 'We find that potential binary star progenitors for SN 2016gkg have smaller pre-SN hydrogen-envelope and helium-core masses than potential single-star progenitors typically by $0.1M_\\odot$ and $2M_\\odot$, respectively. ', 'We find that, a binary companion, if present, is a main-sequence or red-giant star. ', 'We demonstrate that the range of progenitor helium-core mass for SN 2016gkg inferred from observations could help improve constraints on the progenitor. ', 'We find that the probability that the progenitor of SN 2016gkg was a binary is 22\\% when we use constraints only on the progenitor luminosity and effective temperature. Imposing the range of pre-SN progenitor hydrogen-envelope mass and radius inferred from SN light-curves the probability the progenitor is a binary increases to 44\\%. However, there is no clear preference for a binary progenitor. ', '{\\it Conclusions}: We suggest that, at solar metallicity, the stellar wind mass-loss rates are lower than those currently used in most stellar evolution models. Lower mass-loss rates would widen the parameter space for binary Type IIb SNe at solar metallicity by allowing stars that initiate mass transfer earlier in their evolution to reach CC without getting stripped.', 'Our analysis of SN 2016gkg demonstrates the importance of statistical inference methods to constrain progenitor channels.', "Our work indicates that to address the question of progenitors of SNe IIb we still need four pieces of information: (1) SN IIb rates as a function of metallicity, (2) better constraints on structural properties of SN IIb progenitors, (3) robust distributions for single- and binary- star properties, and (4) theoretical models for SN IIb progenitors at solar metallicity using the `correct' mass-loss prescription. ", 'Finally, our work highlights the importance of self-consistent broad parameter space modeling and statistical inference methods to constrain SN progenitor channels. Such methods will be especially important given the deluge of data expected with the imminent launch of Large Synoptic Survey Telescope (LSST).

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  • 10/28/2019
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