An Empirical Fitting Method for Type Ia Supernova Light Curves. II. Estimating the First-light Time and Rise Time

Abstract

We investigate a new empirical fitting method for the optical light curves of Type Ia supernovae (SNe Ia) that is able to estimate the first-light time of SNe Ia, even when they are not discovered extremely early. With an improved ability to estimate the time of first light for SNe Ia, we compute the rise times for a sample of 56 well-observed SNe Ia. We find rise times ranging from 10.5 to 20.5 days, with a mean of 16.0 days, and confirm that the rise time is generally correlated with the decline rate , but with large scatter. The rise time could be an additional parameter to help classify SN Ia subtypes.