Optical Spectropolarimetry and Asphericity of Type Ic SN 2007gr

Understand

We present optical spectropolarimetric observations of Type Ic supernova (SN) 2007gr with Subaru telescope at 21 days after the maximum brightness (~37 days after the explosion).

• Non-zero polarization as high as ~3% is observed at the absorption feature of Ca II IR triplet.
• The polarization of the continuum light is ~0.5% if we estimate the interstellar polarization (ISP) component assuming that the continuum polarization has a single polarization angle.
• This suggests that the axis ratio of the SN photosphere projected to the sky is different from unity by ~10%.