SN 2013ej - A type IIL supernova with weak signs of interaction

TL;DR

This paper presents detailed observations of supernova 2013ej, highlighting its classification as a type IIL supernova with unique spectral and light curve features, and estimates its progenitor characteristics and explosion parameters.

Contribution

It provides comprehensive photometric and spectroscopic analysis of SN 2013ej, revealing its classification as a type IIL supernova and suggesting possible ejecta-CSM interaction and bipolar $^{56}$Ni distribution.

Findings

SN 2013ej has a shorter, steeper plateau phase compared to typical type II SNe.

The estimated $^{56}$Ni mass is significantly lower than in typical type IIP SNe.

Spectral analysis indicates possible ejecta-CSM interaction and bipolar $^{56}$Ni distribution.

Abstract

We present optical photometric and spectroscopic observations of supernova 2013ej. It is one of the brightest type II supernovae exploded in a nearby ($\sim 10$ Mpc) galaxy NGC 628. The light curve characteristics are similar to type II SNe, but with a relatively shorter ($ \sim85 $ day) and steeper ($ \sim1.7 $ mag (100 d)$^{-1} $ in V) plateau phase. The SN shows a large drop of 2.4 mag in V band brightness during plateau to nebular transition. The absolute ultraviolet (UV) light curves are identical to SN 2012aw, showing a similar UV plateau trend extending up to 85 days. The radioactive $^{56}$Ni mass estimated from the tail luminosity is $ 0.02 $M$_{\odot}$ which is significantly lower than typical type IIP SNe. The characteristics of spectral features and evolution of line velocities indicate that SN 2013ej is a type II event. However, light curve characteristics and some spectroscopic features provide strong support in classifying it as a type IIL event. A detailed SYNOW modelling of spectra indicates the presence of some high velocity components in H$\alpha$ and H$\beta$ profiles, implying possible ejecta-CSM interaction. The nebular phase spectrum shows an unusual notch in the H$\alpha$ emission which may indicate bipolar distribution of $^{56}$Ni. Modelling of the bolometric light curve yields a progenitor mass of $ \sim14 $M$_{\odot}$ and a radius of $ \sim450 $R$_{\odot}$, with a total explosion energy of $ \sim2.3\times10^{51} $ erg.