Observational Predictions for Sub-Chandrasekhar Mass Explosions: Further Evidence for Multiple Progenitor Systems for Type Ia Supernovae

Abstract

We present a numerical parameter survey of sub-Chandrasekhar mass white dwarf (WD) explosions. Carbon-oxygen WDs accreting a helium shell have the potential to explode in the sub-Chandrasekhar mass regime. Previous studies have shown how the ignition of a helium shell can either directly ignite the WD at the core-shell interface or propagate a shock wave into the the core causing a central ignition. We examine the explosions of WDs from 0.6 -1.2 M ⊙ with helium shells of 0.01, 0.05 and 0.08 M ⊙ . Distinct observational signatures of sub-Chandrasekhar mass WD explosions are predicted for two categories of shell size. Thicker-shell models show an early time flux excess, which is caused by the presence of radioactive material in the ashes of the helium shell, and red colors due to these ashes creating significant line blanketing in the UV through the blue portion of the spectrum. Thin shell models reproduce several typical Type Ia supernova signatures. We identify a relationship between Si II velocity and luminosity which, for the first time, identifies a sub-class of observed supernovae that are consistent with these models. This sub-class is further delineated by the absence of carbon in their atmospheres. We suggest that the proposed difference in the ratio of selective to total extinction between the high velocity and normal velocity Type Ia supernovae is not due to differences in the properties of the dust around these events, but is rather an artifact of applying a single extinction correction to two intrinsically different populations of supernovae.

Linear spectropolarimetry of 35 Type Ia supernovae with VLT/FORS: an analysis of the Si ii line polarization

“…(iv) However, a comparison of our sample in the ∆m 15 v Si ii plane to numerical predictions for double-detonation explosions (Polin et al 2019) revealed that there are two distinct subgroups. The SNe that fall uniformly above the sub-Chandrasekhar double-detonation explosion model predictions line display higher polarization degrees of the Si ii line compared to a distinct "cluster" of normal Chandrasekharlike SNe (see Figs.…”

“…15a); and those that are suggested to be sub-Chandrasekhar mass white dwarfs (and fall above the prediction, green diamonds). Interestingly, the supernovae with higher polarization of the Si ii line tend to lie above the numerical ∆m 15 -v Si ii predictions for sub-Chandrasekhar mass explosions by Polin et al (2019), compared to supernovae in the "cluster", below the ∆m 15v Si ii line (Fig. 15a), that have lower polarization degrees of the Si ii line.…”

“…Although the off-center delayed detonation explosion scenario provides a good explanation of the observations, a double-detonation scenario cannot be excluded. Polin et al (2019) perform an analysis of the numerical parameter space of 1-D sub-Chandrasekhar mass white dwarf explosion models and found a correlation between mass, brightness and the Si ii velocity exhibited in these double-detonation models with thin helium shells. Polin et al (2019) predicted the Si ii line velocity as function of the absolute peak brightness in B-band, M B , for sub-Chandrasekhar white dwarfs with a thin 0.01 M He shell and a range of white dwarf masses (see Fig.…”

“…Polin et al (2019) predicted the Si ii line velocity as function of the absolute peak brightness in B-band, M B , for sub-Chandrasekhar white dwarfs with a thin 0.01 M He shell and a range of white dwarf masses (see Fig. 11 in Polin et al 2019). In Fig.…”

ZTF Early Observations of Type Ia Supernovae. I. Properties of the 2018 Sample

“…Simulations of the double detonation of a helium shell on the surface of a WD predict an unusually red excess well before peak luminosity (Noebauer et al 2017;Maeda et al 2018;Polin et al 2019), which were observed in SN 2016jhr (Jiang et al 2017) and SN 2018byg (De et al 2019). Should the SD channel hold, a collision between the SN ejecta and the stellar companion will give rise to strong ultraviolet (UV) emission at early times (Kasen 2010;Hayden et al 2010a).…”