On The Intrinsic Diversity of Type II-Plateau Supernovae

TL;DR

This study reveals that Type II-Plateau supernovae exhibit significant intrinsic diversity and complex parameter correlations, influenced by progenitor properties and observational uncertainties, challenging simplified models of their explosion physics.

Contribution

The paper introduces a comprehensive, self-consistent multi-band modeling approach that uncovers the intrinsic width and covariance structure of supernova parameters, highlighting the diversity of progenitor properties.

Findings

Strong covariances among supernova parameters reduce correlation significance.

Intrinsic width of correlations is about 0.25 dex, mainly due to progenitor differences.

Degeneracies in light curve physics lead to weak correlations between explosion energy and ejecta mass.

Abstract

Hydrogen-rich Type II-Plateau supernovae exhibit correlations between the plateau luminosity $L_{\rm pl}$, the nickel mass $M_{\rm Ni}$, the explosion energy $E_{\rm exp}$, and the ejecta mass $M_{\rm ej}$. Using our global, self-consistent, multi-band model of nearby well-observed supernovae, we find that the covariances of these quantities are strong and that the confidence ellipsoids are oriented in the direction of the correlations, which reduces their significance. By proper treatment of the covariance matrix of the model, we discover a significant intrinsic width to the correlations between $L_{\rm pl}$, $E_{\rm exp}$, and $M_{\rm Ni}$, where the uncertainties due to the distance and the extinction dominate. For fixed $E_{\rm exp}$, the spread in $M_{\rm Ni}$ is about 0.25 dex, which we attribute to the differences in the progenitor internal structure. We argue that the effects of incomplete $\gamma$-ray trapping are not important in our sample. Similarly, the physics of the Type II-Plateau supernova light curves leads to inherently degenerate estimates of $E_{\rm exp}$ and $M_{\rm ej}$, which makes their observed correlation weak. Ignoring the covariances of supernova parameters or the intrinsic width of the correlations causes significant biases in the slopes of the fitted relations. Our results imply that Type II-Plateau supernova explosions are not described by a single physical parameter or a simple one-dimensional trajectory through the parameter space, but instead reflect the diversity of the core and surface properties of their progenitors. We discuss the implications for the physics of the explosion mechanism and possible future observational constraints.