Three-Dimensional Explosion Geometry of Stripped-Envelope Core-Collapse Supernovae. I. Spectropolarimetric Observations

TL;DR

This study uses spectropolarimetric observations of stripped-envelope supernovae to reveal that three-dimensional, non-axisymmetric geometries are common in their ejecta, with implications for understanding explosion mechanisms.

Contribution

It provides the first detailed spectropolarimetric analysis of multiple stripped-envelope SNe, demonstrating the prevalence of 3D geometries in their ejecta.

Findings

Most observed stripped-envelope SNe show non-axisymmetric 3D geometries.

Stronger spectral lines tend to exhibit higher polarization.

Dispersion in polarization suggests clumpy ion distributions viewed from different angles.

Abstract

We study the multi-dimensional geometry of supernova (SN) explosions by means of spectropolarimetric observations of stripped-envelope SNe, i.e., SNe without a H-rich layer. We perform spectropolarimetric observations of 2 stripped-envelope SNe, the Type Ib SN 2009jf and the Type Ic SN 2009mi. Both objects show non-zero polarization at the wavelength of the strong lines. They also show a loop in the Stokes Q-U diagram, which indicates a non-axisymmetric, three-dimensional ion distribution in the ejecta. We show that five out of six stripped-envelope SNe which have been observed spectropolarimetrically so far show such a loop. This implies that a three-dimensional geometry is common in stripped-envelope SNe. We find that stronger lines tend to show higher polarization. This effect is not related to the geometry, and must be corrected to compare the polarization of different lines or different objects. Even after the correction, however, there remains a dispersion of polarization degree among different objects. Such a dispersion might be caused by three-dimensional clumpy ion distributions viewed from different directions.