Luminous type IIP SN 2013ej with high-velocity Ni-56 ejecta

TL;DR

This study analyzes the peculiar luminosity evolution of type IIP supernova 2013ej, revealing asymmetric Ni-56 ejecta with high velocities and polarization, which explains discrepancies in hydrodynamic models.

Contribution

It introduces a model accounting for asymmetric bipolar Ni-56 ejecta to explain supernova luminosity and polarization features, addressing previous modeling inconsistencies.

Findings

Ejecta mass of 23-26 Msun and kinetic energy of (1.2-1.4)x10^51 erg determined.

Ni-56 ejecta is asymmetric with a heavier jet in the rear hemisphere.

Predicted polarization matches observational data.

Abstract

We explore the well-observed type IIP SN 2013ej with peculiar luminosity evolution. It is found that the hydrodynamic model cannot reproduce in detail the bolometric luminosity at both the plateau and the radioactive tail. Yet the ejecta mass of 23-26 Msun and the kinetic energy of (1.2-1.4)x10^51 erg are determined rather confidently. We suggest that the controversy revealed in hydrodynamic simulations stems from the strong asphericity of the Ni-56 ejecta. An analysis of the asymmetric nebular H-alpha line and of the peculiar radioactive tail made it possible to recover parameters of the asymmetric bipolar Ni-56 ejecta with the heavier jet residing in the rear hemisphere. The inferred Ni-56 mass is 0.039 Msun, twice as large compared to a straightforward estimate from the bolometric luminosity at the early radioactive tail. The bulk of ejected Ni-56 has velocities in the range of 4000-6500 km/s. The linear polarization predicted by the model with the asymmetric ionization produced by bipolar Ni-56 ejecta is consistent with the observational value.