Supernova 2013by: A Type IIL Supernova with a IIP-like light curve drop

TL;DR

This study presents detailed observations of SN 2013by, revealing a sharp light curve drop characteristic of SNe IIP, suggesting a new way to classify Type II supernovae based on this feature.

Contribution

The paper demonstrates that SNe IIL can exhibit a light curve drop similar to SNe IIP, proposing this as a new physical parameter for subclassification.

Findings

SN 2013by shows a sharp light curve decline after maximum.

Spectra indicate asymmetric lines and high-velocity hydrogen.

Late spectra reveal oxygen lines, implying ejecta mixing.

Abstract

We present multi-band ultraviolet and optical light curves, as well as visual-wavelength and near-infrared spectroscopy of the Type II linear (IIL) supernova (SN) 2013by. We show that SN 2013by and other SNe IIL in the literature, after their linear decline phase that start after maximum, have a sharp light curve decline similar to that seen in Type II plateau (IIP) supernovae. This light curve feature has rarely been observed in other SNe IIL due to their relative rarity and the intrinsic faintness of this particular phase of the light curve. We suggest that the presence of this drop could be used as a physical parameter to distinguish between subclasses of SNe II, rather than their light curve decline rate shortly after peak. Close inspection of the spectra of SN 2013by indicate asymmetric line profiles and signatures of high-velocity hydrogen. Late (less than 90 days after explosion) near-infrared spectra of SN 2013by exhibit oxygen lines, indicating significant mixing within the ejecta. From the late-time light curve, we estimate that 0.029 solar mass of 56Ni was synthesized during the explosion. It is also shown that the V -band light curve slope is responsible for part of the scatter in the luminosity (V magnitude 50 days after explosion) vs. 56Ni relation. Our observations of SN 2013by and other SNe IIL through the onset of the nebular phase indicate that their progenitors are similar to those of SNe IIP.