Bump Morphology of the CMAGIC Diagram

We apply the color-magnitude intercept calibration method (CMAGIC) to the Nearby Supernova Factory SNe Ia spectrophotometric data set. The currently existing CMAGIC parameters are the slope and intercept of a straight line fit to the 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 linear region, beta ( XY ), 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 1D simulations, we show that the correlation between the size of the bump feature and beta ( XY ) can be understood as a result of chemical mixing due to large-scale Rayleigh-Taylor instabilities.

Automated summary

We apply the CMAGIC method to the Nearby Supernova Factory SNe Ia data set and find a significant correlation between the slope of the linear region in the CMAGIC diagram and the size of the bump feature near maximum brightness. These results provide an advantage over extinction-affected parameters defined as a function of time, and the bump size parameter is computed independently of templates. The correlation between bump size and slope can be explained by chemical mixing due to large-scale Rayleigh-Taylor instabilities in 1D simulations.