Improving Cosmological Distance Measurements Using Twin Type Ia Supernovae

TL;DR

This paper presents a new spectrophotometric twin supernova method that reduces brightness dispersion, potentially improving cosmological distance measurements and understanding supernova variability.

Contribution

It introduces a novel twin supernova identification technique using spectrophotometry, leading to improved standardization of Type Ia supernovae for cosmology.

Findings

Standardized supernovae to 0.083 magnitudes dispersion.

Matched spectra pairs show reduced brightness variance.

Method could achieve 0.06-0.07 magnitudes standardization at high redshift.

Abstract

We introduce a method for identifying "twin" Type Ia supernovae, and using them to improve distance measurements. This novel approach to Type Ia supernova standardization is made possible by spectrophotometric time series observations from the Nearby Supernova Factory (SNfactory). We begin with a well-measured set of supernovae, find pairs whose spectra match well across the entire optical window, and then test whether this leads to a smaller dispersion in their absolute brightnesses. This analysis is completed in a blinded fashion, ensuring that decisions made in implementing the method do not inadvertently bias the result. We find that pairs of supernovae with more closely matched spectra indeed have reduced brightness dispersion. We are able to standardize this initial set of SNfactory supernovae to 0.083 +/- 0.012 magnitudes, implying a dispersion of 0.072 +/- 0.010 magnitudes in the absence of peculiar velocities. We estimate that with larger numbers of comparison SNe, e.g, using the final SNfactory spectrophotometric dataset as a reference, this method will be capable of standardizing high-redshift supernovae to within 0.06-0.07 magnitudes. These results imply that at least 3/4 of the variance in Hubble residuals in current supernova cosmology analyses is due to previously unaccounted-for astrophysical differences among the supernovae