A NOVEL COLOR PARAMETER AS A LUMINOSITY CALIBRATOR FOR TYPE Ia SUPERNOVAE

摘要

Type Ia supernovae (SNe Ia) provide us with a unique tool for measuring extragalactic distances and determining cosmological parameters. As a result, the precise and effective calibration for peak luminosities of SNe Ia becomes extremely crucial and thus is critically scrutinized for cosmological explorations. In this Letter, we reveal clear evidence for a tight linear correlation between peak luminosities of SNe Ia and their B — V colors ～ 12 days after the B maximum denoted by ΔC_(12). By introducing such a novel color parameter, ΔC_(12), this empirical correlation allows us to uniformly standardize SNe Ia with decline rates Δm_(15) in the range of 0.8 < Δm_(15) < 2.0 and to reduce scatters in estimating their peak luminosities from ～0.5 mag to the levels of 0.18 and 0.12 mag in the V and / bands, respectively. For a sample of SNe Ia with insignificant reddenings of host galaxies [e.g., E(B -V)_(host) approx< 0.06 mag], the scatter drops further to only 0.07 mag (or 3%-4% in distance), which is comparable to observational accuracies and is better than other calibrations for SNe Ia. This would impact observational and theoretical studies of SNe Ia and cosmological scales and parameters.