Diversity of Luminous Supernovae from Non-Steady Mass Loss

TL;DR

This paper explains the spectral diversity of luminous Type II supernovae through variations in the density slope of their surrounding dense wind caused by non-steady mass loss, affecting observable spectral features.

Contribution

It introduces a model linking wind density structure to supernova spectral types, explaining why some LSNe show wind signatures while others do not.

Findings

The ratio of diffusion to shock timescales depends on the wind density slope w.

Type IIL LSNe have comparable diffusion and shock timescales, explaining the absence of wind features.

Type IIn LSNe have longer shock propagation, showing wind signatures in spectra.

Abstract

We show that the diversity in the density slope of the dense wind due to non-steady mass loss can be one way to explain the spectral diversity of Type II luminous supernovae (LSNe). The interaction of SN ejecta and wind surrounding it is considered to be a power source to illuminate LSNe because many LSNe show the wind signature in their spectra (Type IIn LSNe). However, there also exist LSNe without the spectral features caused by the wind (Type IIL LSNe). We show that, even if LSNe are illuminated by the interaction, it is possible that they do not show the narrow spectra from the wind if we take into account of non-steady mass loss of their progenitors. When the shock breakout takes place in the dense wind with the density structure \rho\propto r^{-w}, the ratio of the diffusion timescale in the optically thick region of the wind (td) and the shock propagation timescale of the entire wind after the shock breakout (ts) strongly depends on w. For the case w<~1, both timescales are comparable (td/ts \simeq 1) and td/ts gets smaller as w gets larger. For the case td/ts\simeq 1, the shock goes through the entire wind just after the light curve (LC) peak and narrow spectral lines from the wind cannot be observed after the LC peak (Type IIL LSNe). If td/ts is much smaller, the shock wave continues to propagate in the wind after the LC peak and unshocked wind remains (Type IIn LSNe). This difference can be obtained only through a careful treatment of the shock breakout condition in a dense wind. The lack of narrow Lorentzian line profiles in Type IIL LSNe before the LC peak can also be explained by the difference in the density slope. Furthermore, we apply our model to Type IIn LSN 2006gy and Type IIL LSN 2008es and find that our model is consistent with the observations.