A Precise Distance Indicator: Type Ia Supernova Multicolor Light‐Curve Shapes

TLDR

The study introduces an empirical method using multicolor light‑curve shapes to estimate the luminosity, distance, and extinction of Type Ia supernovae. The method derives a correlation between MLCSs and luminosity from a training set of nine supernovae, applies Bayesian extinction estimation, and uses both light‑curve and color data to distinguish distance, intrinsic dimness, and dust extinction, with precision tested against a Hubble diagram of 20 additional supernovae. The analysis shows that dimmer Type Ia supernovae are redder and decline faster, intrinsic color variations vanish after 35 days, and the MLCS method achieves a 5 % distance accuracy with a Hubble constant of 64 ± 3 km s⁻¹ Mpc⁻¹, confirming the linearity of the Hubble law.

Abstract

We present an empirical method that uses multicolor light-curve shapes (MLCSs) to estimate the luminosity, distance, and total line-of-sight extinction of Type Ia supernovae (SNe Ia). The empirical correlation between the MLCSs and the luminosity is derived from a " training set" of nine SN Ia light curves with independent distance and reddening estimates. We find that intrinsically dim SN Ia's are redder and have faster light curves than the bright ones, which are slow and blue. By 35 days after maximum, the intrinsic color variations become negligible. A formal treatment of extinction employing Bayes's theorem is used to estimate the best value and its uncertainty. Applying the MLCS method to both light curves and to color curves provides enough information to determine which supernovae are dim because they are distant, which are intrinsically dim, and which are dim because of extinction by dust. The precision of the MLCS distances is examined by constructing a Hubble diagram with an independent set of 20 SN Ia's. The dispersion of 0.12 mag indicates a typical distance accuracy of 5% for a single object, and the intercept yields a Hubble constant on the Sandage et al. Cepheid distance scale of H0 = 64 ± 3 (statistical) km s–1 Mpc–1 (±6 total error). The slope of 0.2010 ± 0.0035 mag over the distance interval 32.2 < μ < 38.3 yields the most precise confirmation of the linearity of the Hubble law.