The type Ia supernova width-luminosity relation

Observations of type Ia supernov ae at high redshifts have become an import ant tool for studying the geometry of the universe. The relation between th e duration of the peak phase of a type Ia supernova's lightcurve and its lu minosity (broader is brighter) forms the cornerstone of this measurement, y et it is a purely empirical relation. In this paper we show that the relati on is a natural consequence of the radiation transport in type Ia supernova e and suggest constraints on the nature of the explosions which arise from our interpretation of the observed relation. The principle parameter underl ying the relation is the mass of radioactive Ni-56 produced in the explosio n. The relation is shown to be relatively insensitive to most other paramet ers in Chandrasekhar-mass explosions. Cosmological results are thus unlikel y to suffer from systematic effects stemming from evolution in the explosio ns' progenitors. (C) 2001 Published by Elsevier Science B. V.