SN IA light curves and radioactive decay

Abstract

The absolute V light curves of 5 SNe Ia, selected to represent the known range of absolute luminosities at maximum for this class of objects, are presented. Comparison of the long term luminosity evolution shows that the differences seen at maximum persist, and actually increase with time, reinforcing the notion that intrinsic differences do exist among SNe Ia. Since such differences are not accounted for in the standard progenitor scenario, it becomes important to derive constraints for the models directly from the observations. In order to investigate the influence of the two most important parameters, that is the masses of the synthesized radioactive material and of the ejecta, a simple MC light curve model was used to simulate the luminosity evolution from the explosion to very late epochs ( ~ 1000 days). It was found that the observations require a range of a factor 10 in the masses of the radioactive material synthesized in the explosion (M_Ni = 0.1-1.1 M_sun,) and a factor 2 in the total mass of the ejecta (M_ej = 0.7-1.4 M_sun). Differences of a factor 2 in M_Ni seem to be present even among `normal' SNe Ia. Some evidence was also found that the deposition of the positrons from Co decay varies from object to object, and with time. In particular, the latest HST observations of SN 1992A seem to imply complete trapping of the positrons. Based on ESO observations collected at ESO-La Silla (Chile)