Asymmetries in the Type IIn SN2010jl

TL;DR

This study uses optical spectropolarimetry to reveal that SN2010jl exhibits significant asphericity and a well above the photosphere line forming region, providing insights into its explosion geometry and environment.

Contribution

It provides the first detailed spectropolarimetric analysis of SN2010jl, demonstrating its asphericity and comparing its polarization features with other Type IIn supernovae.

Findings

Continuum polarization of 1.7-2.0% indicates substantial asphericity.

Line depolarization at Halpha and Hbeta suggests line forming regions are above the photosphere.

Low interstellar polarization implies minimal dust in the progenitor environment.

Abstract

Aims: We study possible signs of asymmetry in the luminous Type IIn SN2010jl, to obtain independent information on the explosion geometry. Methods: We obtained optical linear spectropolarimetry of SN2010jl two weeks after the discovery, in the spectral range 3700-8800 A. Results: The object exhibits a continuum polarization at a very significant and almost constant level (1.7-2.0%). Marked line depolarization is seen at the positions of the strongest emission features, like Halpha and Hbeta. This implies that the line forming region is well above the photosphere. The continuum polarization level (1.7-2.0%) indicates a substantial asphericity, of axial ratio <=0.7. The almost complete depolarization seen at Halpha suggests a very low level of interstellar polarization (<=0.3%). This rules out the presence of relevant amounts of dust in the progenitor environment at the time of our observations. From a polarimetric point of view, SN2010jl appears to be very similar to the two other well studied Type IIn SNe 1997eg and 1998S, establishing a strong link within this class of objects.