Bump Morphology of the CMAGIC Diagram

TL;DR

This paper introduces a new parameter, $oldsymbol{omega_{XY}}$, characterizing the bump feature in the CMAGIC diagram of SNe Ia, revealing correlations with existing parameters and implications for supernova physics.

Contribution

The study defines a novel bump size parameter in the CMAGIC diagram and explores its correlation with the slope, enhancing supernova analysis methods.

Findings

Significant correlation between slope $eta_{XY, 1}$ and bump size $omega_{XY}$.

Current empirical templates, especially SALT3, reproduce the observed features.

Simulations suggest the bump-slope correlation results from chemical mixing due to Rayleigh-Taylor instabilities.

Abstract

We apply the color-magnitude intercept calibration method (CMAGIC) to the Nearby Supernova Factory SNe Ia spectrophotometric dataset. The currently existing CMAGIC parameters are the slope and intercept of a straight line fit to the first linear region in the color-magnitude diagram, which occurs over a span of approximately 30 days after maximum brightness. We define a new parameter, $\omega_{XY}$, the size of the ``bump'' feature near maximum brightness for arbitrary filters $X$ and $Y$. We find a significant correlation between the slope of the first linear region, $\beta_{XY, 1}$, in the CMAGIC diagram and $\omega_{XY}$. These results may be used to our advantage, as they are less affected by extinction than parameters defined as a function of time. Additionally, $\omega_{XY}$ is computed independently of templates. We find that current empirical templates are successful at reproducing the features described in this work, particularly SALT3, which correctly exhibits the negative correlation between slope and bump size seen in our data. In 1-D simulations, we show that the correlation between the size of the bump feature and $\beta_{XY, 1}$ can be understood as a result of chemical mixing due to large-scale Rayleigh-Taylor instabilities.