Universality in SNIae and the Phillips Relation

The use of supernovae of Type Ia for the determination of accurate distances rests upon the empirical Phillips relation, in which the brightest events are the broadest in time. Implications of new data upon the homogeneity of light curves under the operation of a stretch in time, of the parabolic luminosity increase at the earliest times, and of the time from explosion to maximum light are discussed. The early luminosity is in excellent agreement with predictions (Arnett 1982), and the lack of prominent higher modes of diffusion constrain progenitor and explosion models. Difficulties with reproducing the observed rise time are restricted to radiative transfer models (e.g., Hoeflich and Khokhlov), and probably due to an overestimate of thermal photon escape due to inadequate line lists. Because of the strong dependence of luminosity on 56Ni mass, some simple models can give a Phillips relation of the correct sense.