Standard type Ia supernovae derive their energy from a runaway nuclear fusion of a carbon-oxygen white dwarf. The details of the energetics are still not fully understood, but the result is the ejection of the entire mass of the original star at high kinetic energy. Around half a solar mass of that mass is Ni generated from silicon burning. Ni is radioactive and decays into Co by beta plus decay (with a half life of six days) and gamma rays. Co itself decays by the beta plus (positron) path with a half life of 77 days into stable Fe. These two processes are responsible for the electromagnetic radiation from type Ia supernovae. In combination with the changing transparency of the ejected material, they produce the rapidly declining light curve.