1999AJ....118.2668R

We have compared the rise time for samples of nearby and high-redshift Type Ia supernovae (SNe Ia). The fiducial rise time of the nearby SNe Ia is 2.5±0.4 days longer than the preliminary measurement of the rise time in 1998 by Goldhaber and by Groom for high-redshift SNe Ia from the Supernova Cosmology Project. If further analysis of the high-redshift data does not lead to a significant change in the value or uncertainty in the rise time, then the statistical likelihood that the two samples have different fiducial rise times remains high (5.8 σ) and indicates possible evolution between the samples of SNe Ia. We consider the likely effects of several sources of systematic error, but none of these resolves the difference in the rise times. Currently, we cannot directly determine the impact of the apparent evolution on previous determinations of cosmological parameters.