2006ApJ...641...50W

Published B and V fluxes from nearby Type Ia supernovae (SNe) are fitted to light-curve templates with four to six adjustable parameters. Separately, B magnitudes from the same sample are fitted to a linear dependence on B-V color within a postmaximum time window prescribed by the CMAGIC method. These fits yield two independent SN magnitude estimates B_maxand B_BV. Their difference varies systematically with decline-rate Δm₁₅in a form that is compatible with a bilinear but not a linear dependence; a nonlinear form likely describes the decline-rate dependence of B_maxitself. A Hubble fit to the average of B_max and B_BVrequires a systematic correction for observed B-V color that can be described by a linear coefficient R=2.59±0.24, well below the coefficient R_B~4.1 commonly used to characterize the effects of Milky Way dust. At 99.9% confidence the data reject a simple model in which no color correction is required for SNe that are clustered at the blue end of their observed color distribution. After systematic corrections are performed, B_maxand B_BVexhibit mutual rms intrinsic variation equal to 0.074±0.019 mag, of which at least an equal share likely belongs to B_BV. SN magnitudes measured using maximum luminosity or CMAGIC methods show comparable rms deviations of order ~0.14 mag from the Hubble line. The same fit also establishes a 95% confidence upper limit of 486 km/s on the rms peculiar velocity of nearby SNe relative to the Hubble flow.