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

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$α$ and H$β$ profiles, implying possible ejecta-CSM interaction. The nebular phase spectrum shows an unusual notch in the H$α$ 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.

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