The Rise Time of Nearby Type IA Supernovae

We present calibrated photometric measurements of the earliest detections of nearby Type Ia supernovae (SNe Ia). The set of ~30 new, unfiltered CCD observations delineate the early rise behavior of SNe Ia 18 to 10 days before maximum. Using simple empirical models, we demonstrate the strong correlation between the rise time (i.e., the time between explosion and maximum), the postrise light-curve shape, and the peak luminosity. Using a variety of light-curve shape methods, we find the rise time to B maximum for an SN Ia with Δm₁₅(B)=1.1 mag and peak M_V=-19.45 mag to be 19.5+/-0.2 days. We find that the peak brightness of SNe Ia is correlated with their rise time; SNe Ia that are 0.10 mag brighter at peak in the B band require 0.80+/-0.05 days longer to reach maximum light. We determine the effects of several possible sources of systematic errors, but none of these significantly impacts the inferred rise time. We explore the degree to which comparisons between the observed and theoretically predicted rise times constrain SN Ia progenitor systems.