Spectropolarimetry of stripped envelope core collapse supernovae and their progenitors

TL;DR

This paper presents new spectropolarimetric data for stripped envelope supernovae, analyzes their complex geometries, explores potential jet signatures, and discusses the limitations of current modeling approaches.

Contribution

It provides the most complete spectropolarimetric datasets for certain supernova types and evaluates the effectiveness of simple geometric models, highlighting their degeneracies and limitations.

Findings

Spectropolarimetry reveals complex and varied geometries in stripped envelope supernovae.

Potential jet signatures were identified in SN 2014ad.

Simple geometric models suffer from degeneracies and may not accurately interpret spectropolarimetric data.

Abstract

Over the past 30 years, spectropolarimetry has proven to be a great tool to probe the 3D geometry of core collapse supernovae (CCSNe). The number of high-quality multi-epoch spectropolarimetric data sets for CCSNe remains quite low, however, due to the challenging nature of such observations. In this Thesis we present and analyse the data of two Type IIb SNe (SN 2008aq - two epochs, SN 2011hs - seven epochs) and one Type Ic-bl (SN 2014ad - seven epochs). The latter is the most complete spectropolarimetric data set for a Type Ic-bl to date. We also provide a preliminary re-analysis of the spectropolarimetric data of SN 1993J. The new datasets demonstrate that the spectropolarimetry of stripped envelope supernovae is complex and varied, and although early studies of type IIb SNe showed similar behaviour to type IIP, it is now clear that this early trend is broken by a growing sample of SNe. Additionally, we identified potential signatures of a jet in SN 2014ad. Furthermore, a toy model to simulate spectropolarimetry from simple geometries (similar to Reilly et al. 2016) was created. A systematic approach to parameter space exploration was developped; this showed that unfortunately these models suffer extreme degeneracies and may not lead to accurate interpretations. Finally, spectropolarimetry can also be used to probe asymmetries caused by fast rotation in the potential progenitors of stripped envelope CCSNe. Although numerous Wolf-Rayet stars of type WN and WC have been observed with spectropolarimetry, no single WO stars have been studied to date. In our data of two Galactic WO stars, we found no line effect and could not sufficiently constrain the rotational velocity to exclude a collapsar scenario. Therefore, the absence of a line effect may not necessarily equate to a low rotational velocity.