Epochs of maximum light and bolometric light curves of type Ia supernovae

We present empirical fits to the UBVRI light curves of type Ia supernovae. These fits an used to objectively evaluate tight curve parameters. We find that the relative times of maximum light in the filter passbands are very s imilar for most objects. Surprisingly the maximum at longer wavelengths is reached earlier than in the B and V light curves. This clearly demonstrates the complicated nature of the supernova emission. Bolometric light curves for a small sample of well-observed SNe Ia are cons tructed by integration over the optical filters. In most objects a plateau or inflection is observed in the light curve about 20-40 days after bolomet ric maximum. The strength of this plateau varies considerably among the ind ividual objects in the sample. Furthermore the rise times show a range of s everal days for the few objects which have observations early enough for su ch an analysis. On the other hand, the decline rate between 50 and 80 days past maximum is remarkably similar for all objects, with the notable except ion of SN 1991bg. The similar late decline rates for the supernovae indicat e that the energy release at late times are very uniform; the differences a t early times an likely due to the radiation diffusing out of the ejecta. With the exception of SN 1991bg, the range of absolute bolometric luminosit ies of SNe Ia is found to be at least a factor of 2.5. The nickel masses de rived from this estimate range from 0.4 to 1.1 M-circle dot. It seems impos sible to explain such a mass range by a single explosion mechanism, especia lly since the rate of gamma-ray escape at late phases seems to be very unif orm.