SN 2013ej in M74: A Luminous and Fast-declining Type II-P Supernova

TL;DR

SN 2013ej is a luminous, fast-declining Type II-P supernova with unique spectral features and explosion parameters, providing insights into the properties of its red supergiant progenitor.

Contribution

This study provides detailed multi-wavelength observations and hydrodynamical modeling of SN 2013ej, revealing its explosion energy, progenitor size, and nickel mass, which are new insights for Type II-P supernovae.

Findings

Higher peak luminosity and faster decline than typical Type IIP supernovae.

Spectral evolution similar to some SNe but with larger expansion velocities.

Explosion energy estimated at ~0.7×10^{51} erg, progenitor radius ~600 R_sun, and ejected mass ~10.6 M_sun.

Abstract

We present extensive ultraviolet, optical, and near-infrared observations of the type IIP supernova (SN IIP) 2013ej in the nearby spiral galaxy M74. The multicolor light curves, spanning from $\sim$ 8--185 days after explosion, show that it has a higher peak luminosity (i.e., M$_{V}$ $\sim$$-$17.83 mag at maximum light), a faster post-peak decline, and a shorter plateau phase (i.e., $\sim$ 50 days) compared to the normal type IIP SN 1999em. The mass of $^{56}$Ni is estimated as 0.02$\pm$0.01 M$_{\odot}$ from the radioactive tail of the bolometric light curve. The spectral evolution of SN 2013ej is similar to that of SN 2004et and SN 2007od, but shows a larger expansion velocity (i.e., $v_{Fe II} \sim$ 4600 km s$^{-1}$ at t $\sim$ 50 days) and broader line profiles. In the nebular phase, the emission of H$\alpha$ line displays a double-peak structure, perhaps due to the asymmetric distribution of $^{56}$Ni produced in the explosion. With the constraints from the main observables such as bolometric light curve, expansion velocity and photospheric temperature of SN 2013ej, we performed hydrodynamical simulations of the explosion parameters, yielding the total explosion energy as $\sim$0.7$\times$ 10$^{51}$ erg, the radius of the progenitor as $\sim$600 R$_{\odot}$, and the ejected mass as $\sim$10.6 M$_{\odot}$. These results suggest that SN 2013ej likely arose from a red supergiant with a mass of 12--13 M$_{\odot}$ immediately before the explosion.