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SN 1993J is one of the best studied Type IIb supernovae. Spectropolarimetricdata analyses were published over two decades ago at a time when the field ofsupernova spectropolarimetry was in its infancy. Here we present a new analysisof the spectropolarimetric data of SN 1993J and an improved estimate of itsinterstellar polarization (ISP) as well as a critical review of ISP removaltechniques employed in the field. The polarization of SN 1993J is found to showsignificant alignment on the $q-u$ plane, suggesting the presence of a dominantaxis and therefore of continuum polarization. We also see strong linepolarization features, including $\mathrm{H\beta}$, He\,{\sc i} $\lambda 5876$,$\mathrm{H\alpha}$, He\,{\sc i} $\lambda 6678$, He\,{\sc i} $\lambda 7065$, andhigh velocity (HV) components of He\,{\sc i} $\lambda 5876$ and$\mathrm{H\alpha}$. SN 1993J is therefore the second example of a strippedenvelope supernova, alongside iPTF13bvn, with prominent HV helium polarizationfeatures, and the first to show a likely HV \halpha contribution. Overall, wedetermine that the observed features can be interpreted as the superposition ofanisotropically distributed line forming regions over ellipsoidal ejecta. Wecannot exclude the possibility of an off-axis energy source within the ejecta.These data demonstrate the rich structures that are inaccessible if solelyconsidering the flux spectra but can be probed by spectropolarimetricobservations. In future studies, the new ISP corrected data can be used inconjunction with 3D radiative transfer models to better map the geometry of theejecta of SN 1993J.

The shape of SN 1993J re-analyzed