# The 3D shape of Type IIb SN 2011hs

## TL;DR

This study presents detailed spectropolarimetric observations of the Type IIb supernova 2011hs, revealing insights into its 3D ejecta structure and polarization behavior, with implications for understanding supernova geometries.

## Contribution

First spectropolarimetric analysis of SN 2011hs, revealing its 3D ejecta structure and polarization evolution, and comparing it to similar supernovae.

## Key findings

- Detected high interstellar polarization (~3%) likely due to small silicate grains.
- Observed intrinsic continuum polarization at -3 and +2 days.
- Noted a gradual rotation of polarization angle indicating complex ejecta geometry.

## Abstract

We observed seven epochs of spectropolarimetry in optical wavelengths for the Type IIb SN 2011hs, ranging from -3 to +40 days with respect to V -band maximum. A high degree of interstellar polarization was detected (up to ~3 percent), with a peak lying blueward of 4500A. Similar behaviours have been seen in some Type Ia SNe, but had never been observed in a Type IIb. We find that it is most likely the result of a relative enhancement of small silicate grains in the vicinity of the SN. Significant intrinsic continuum polarization was recovered at -3 and +2 days (p = 0.55 +\- 0.12 percent and p = 0.75 +\- 0.11 percent, respectively). We discuss the change of the polarization angle across spectral lines and in the continuum as diagnostics for the 3D structure of the ejecta. We see a gradual rotation by about -50 degree in the continuum polarization angle between -2 and +18 days after V - band maximum. A similar rotation in He I {\lambda}5876, H{\alpha} and the Ca II infrared triplet seems to indicate a strong influence of the global geometry on the line polarization features. The differences in the evolution of their respective loops on the Stokes q - u plane suggest that line specific geometries are also being probed. Possible interpretations are discussed and placed in the context of literature. We find that the spectropolarimetry of SN 2011hs is most similar to that of SN 2011dh, albeit with notable differences.