An analysis of the spectroscopic signatures of layering in the ejecta of type Iax supernovae

TL;DR

This paper investigates whether the ejecta of type Iax supernovae are layered or well-mixed, using models and spectroscopic signatures, and finds that current evidence does not conclusively support layering, leaving the pure deflagration scenario plausible.

Contribution

The study introduces stratified and mixed ejecta models to analyze spectroscopic signatures, challenging previous assumptions about layering in type Iax supernovae.

Findings

Heavily mixed models fit SN 2012Z well

Blending can explain line profile differences

No conclusive evidence for necessary layering

Abstract

Investigations of some type Iax supernovae have led to the suggestion that their ejecta must be layered to some degree. Such an ejecta structure has been argued as inconsistent with the well-mixed composition predicted by pure deflagrations. Based on explosion models, we create toy models in which the ejecta are artificially stratified and progressively mixed until a uniform composition is obtained. We find that models that are heavily mixed, containing burned and unburned material at all velocities, produce reasonably good agreement with SN 2012Z, for which a layered structure has been suggested. We also discuss how existing ejecta compositions determined for type Iax supernovae do not necessarily contradict pure deflagration models and may be consistent with a steeper density profile. We investigate previous claims that differences in line profile shapes may be due to strong blending, by presenting a series of models with different plasma states. These models indicate that blending could indeed explain differences in the observed profiles. Alternatively, stratification could also explain such differences, however all of our models indicate that this does not necessarily require stratification in abundance. Sufficient stratification in ionisation state can be achieved even for a well-mixed model. Based on our analysis, we demonstrate that there is insufficient evidence to suggest the ejecta of type Iax supernovae must be layered and therefore argue the pure deflagration scenario is not ruled out, even for the brightest type Iax supernovae. Our analysis does not indicate the ejecta cannot be layered to some degree, but observations within days of explosion are necessary to determine the extent to which the outer ejecta could be layered.