Spectropolarimetry of stripped envelope core collapse supernovae

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 work 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.
SN 2011hs was found to have a geometry consistent with an off-axis energy source within an ellipsoidal envelope, and features similar to SN 2011dh. In SN 2014ad we showed
the presence of intermediate mass elements in outer parts of the ejecta as well as significant
axi-symmetry, consistent with the presence of a jet. We also provided a re-analysis of
the Type IIb SN 1993J, including a novel estimate of its interstellar polarisation. Diverse
asymmetries were found in all SNe, both in the global geometry of the photosphere and in
the distribution of the line forming regions. They are discussed in the context of previous
studies.
In order to simulate the geometry of the ejecta and the resulting observations, we re-
created a pre-existing toy model, improving on previous work by devising a way to explore
parameter space methodically. We found that such toy models are prone to degeneracies,
and warn that they should be used with great caution, if at all.
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.