Predicting polarization signatures for double-detonation and delayed-detonation models of Type Ia supernovae

TL;DR

This study uses synthetic spectropolarimetry to compare two Type Ia supernova explosion models, finding both produce low polarization levels consistent with normal supernovae, but not with highly polarized extreme cases.

Contribution

It provides detailed polarization predictions for double-detonation and delayed-detonation models, enhancing understanding of supernova explosion asymmetries.

Findings

Both models produce polarization < 1%, matching normal supernovae.

Synthetic Si II line polarization aligns with observations.

Models cannot explain high polarization in extreme supernovae.

Abstract

Calculations of synthetic spectropolarimetry are one means to test multi-dimensional explosion models for Type Ia supernovae. In a recent paper, we demonstrated that the violent merger of a 1.1 and 0.9 M$_{\odot}$ white dwarf binary system is too asymmetric to explain the low polarization levels commonly observed in normal Type Ia supernovae. Here, we present polarization simulations for two alternative scenarios: the sub-Chandrasekhar mass double-detonation and the Chandrasekhar mass delayed-detonation model. Specifically, we study a two-dimensional double-detonation model and a three-dimensional delayed-detonation model, and calculate polarization spectra for multiple observer orientations in both cases. We find modest polarization levels ($<$ 1 per cent) for both explosion models. Polarization in the continuum peaks at $\sim$ 0.1$-$0.3 per cent and decreases after maximum light, in excellent agreement with spectropolarimetric data of normal Type Ia supernovae. Higher degrees of polarization are found across individual spectral lines. In particular, the synthetic Si ii {\lambda}6355 profiles are polarized at levels that match remarkably well the values observed in normal Type Ia supernovae, while the low degrees of polarization predicted across the O i {\lambda}7774 region are consistent with the non-detection of this feature in current data. We conclude that our models can reproduce many of the characteristics of both flux and polarization spectra for well-studied Type Ia supernovae, such as SN 2001el and SN 2012fr. However, the two models considered here cannot account for the unusually high level of polarization observed in extreme cases such as SN 2004dt.