Multicolor Light Curves of Type Ia Supernovae on the Color‐Magnitude Diagram: A Novel Step toward More Precise Distance and Extinction Estimates

Abstract

We show empirically that fits to the color-magnitude relation of Type Ia supernovae after optical maximum can provide accurate relative extragalactic distances. We report the discovery of an empirical color relation for Type Ia light curves: During much of the first month past maximum, the magnitudes of Type Ia supernovae defined at a given value of color index have a very small magnitude dispersion; moreover, during this period the relation between B magnitude and B−V color (or B−R or B−I color) is strikingly linear, to the accuracy of existing well-measured data. These linear relations can provide robust distance estimates, in particular, by using the magnitudes when the supernova reaches a given color. After correction for light curve strech factor or decline rate, the dispersion of the magnitudes taken at the intercept of the linear color-magnitude relation are found to be around 0 m .08 for the sub-sample of supernovae with (B max − V max ) ≤ 0 m .05, and around 0 m .11 for the sub-sample with (B max −V max ) ≤ 0 m .2. This small dispersion is consistent with being mostly due to observational errors. The method presented here and the conventional light curve fitting methods can be combined to further improve statistical dispersions of distance estimates. It can be combined with the magnitude at maximum to deduce dust extinction. The slopes of the color-magnitude relation may also be used to identify intrinsically different SN Ia systems. The method provides a tool that is fundamental to using SN Ia to estimate cosmological parameters such as the Hubble constant and the mass and dark energy content of the universe.

Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope

“…Instead of the value R B $ 4:1 expected for dust extinction in the Galaxy and LMC, values R B $ 2Y3 are often found (Tripp & Branch 1999;Phillips et al 1999;Wang et al 2003Wang et al , 2006Knop et al 2003). In this hypothesis, dust in the immediate vicinity of the SN or at the highest velocities of its ejecta scatters SN light into the observer line of sight, thus adding back light and effectively reducing derived values of R k in the optical.…”

The slowly declining type Ia supernova 2008fv and the near-infrared second maximum

“…Improved relations have been provided by several authors in the past fifteen years, which have also involved a "second" parameter (e.g., the colour (B−V), Tripp 1998;Tripp & Branch 1999;Reindl et al 2005), which provides a tight calibration of the luminosity. Other methods have been Tables 6, 7 and 15 are available in electronic form at http://www.aanda.org developed, such as the multicolour light-curve shape (MLCS) method of Riess et al (1996), the stretch correction methods of Perlmutter et al (1997), the SALT technique by Guy et al (2005), and the CMAGIC technique proposed by Wang et al (2003), who derived the absolute magnitude as a function of colour.…”

The Hubble Constant from Type Ia Supernovae Calibrated with the Linear and Nonlinear Cepheid Period-Luminosity Relations

“…INTRODUCTION Because of their intrinsic brightness at maximum, it is well known that Type Ia supernovae (SNe Ia) can be used to obtain the Hubble constant (H 0 ). Furthermore, the peak brightness of SNe Ia is regarded as a standard candle after one corrects for their light-curve shape [using, e.g., Dm 15 (B), Phillips 1993; the s-factor, Perlmutter et al 1997;MLCS, Riess et al 1996; CMAGIC, Wang et al 2003]. Nevertheless, the peak brightnesses of the supernovae after light-curve shape (and extinction) corrections still need to be calibrated with nearby samples before they can be used to derive the Hubble constant.…”