The shape of SN 1993J re-analyzed
  SN 1993J is one of the best studied Type IIb supernovae. Spectropolarimetric
data analyses were published over two decades ago at a time when the field of
supernova spectropolarimetry was in its infancy. Here we present a new analysis
of the spectropolarimetric data of SN 1993J and an improved estimate of its
interstellar polarization (ISP) as well as a critical review of ISP removal
techniques employed in the field. The polarization of SN 1993J is found to show
significant alignment on the $q-u$ plane, suggesting the presence of a dominant
axis and therefore of continuum polarization. We also see strong line
polarization features, including $\mathrm{H\beta}$, He\,{\sc i} $\lambda 5876$,
$\mathrm{H\alpha}$, He\,{\sc i} $\lambda 6678$, He\,{\sc i} $\lambda 7065$, and
high velocity (HV) components of He\,{\sc i} $\lambda 5876$ and
$\mathrm{H\alpha}$. SN 1993J is therefore the second example of a stripped
envelope supernova, alongside iPTF13bvn, with prominent HV helium polarization
features, and the first to show a likely HV \halpha contribution. Overall, we
determine that the observed features can be interpreted as the superposition of
anisotropically distributed line forming regions over ellipsoidal ejecta. We
cannot exclude the possibility of an off-axis energy source within the ejecta.
These data demonstrate the rich structures that are inaccessible if solely
considering the flux spectra but can be probed by spectropolarimetric
observations. In future studies, the new ISP corrected data can be used in
conjunction with 3D radiative transfer models to better map the geometry of the
ejecta of SN 1993J.
