Broad band polarimetric investigation of Type IIP supernova 2013ej

TL;DR

This study presents polarimetric observations of supernova 2013ej, revealing significant intrinsic polarization indicative of asymmetrical ejecta, with implications for understanding supernova explosion geometries.

Contribution

First detailed polarimetric analysis of SN 2013ej showing high intrinsic polarization, suggesting asymmetric ejecta in a Type IIP supernova.

Findings

Maximum intrinsic polarization of 2.14% observed.

Intrinsic polarization exceeds foreground star polarization.

Asymmetry in ejecta inferred from polarization data.

Abstract

We present results based on follow-up observations of the Type II-plateau supernova (SN) 2013ej at 6 epochs spanning a total duration of $\sim$37 d. The $R_{c}$-band linear polarimetric observations were carried out between the end of the plateau and the beginning of the nebular phases as noticed in the photometric light curve. The contribution due to interstellar polarization (ISP) was constrained by using couple of approaches, i.e. based upon the observations of foreground stars lying within 5\arcmin\, and 10$\degr$ radius of the SN location and also investigating the extinction due to the Milky Way and host galaxy towards the SN direction. Our analysis revealed that in general the intrinsic polarization of the SN is higher than the polarization values for the foreground stars and exhibits an increasing trend during our observations. After correcting the ISP of $\sim$0.6 per cent, the maximum intrinsic polarization of SN~2013ej is found to be 2.14 $\pm$ 0.57 per cent. Such a strong polarization has rarely been seen in Type II-P SNe. If this is the case, i.e., the `polarization bias' effect is still negligible, the polarization could be attributed to the asymmetry of the inner ejecta of the SN because the ISP towards the SN location is estimated to be, at most, 0.6 per cent.