Radiation Energy-Balance Method for Calculating the Time Evolution of Type Ia Supernovae During the Post-Explosion Phase

A new method is presented for calculating the time evolution of spherically symmetric Type Ia Supernova in the post-explosion phase, enabling light curves and spectra to be simulated in a physically self-consistent way. The commonly exploited radiative equilibrium, that is in essence a /gas energy balance/ condition, is unsuitable for this purpose for important physical and numerical reasons. Firstly, the RE depends on the heating and cooling rates of the gas by the radiation field, two quantities that almost completely cancel and are very difficult to calculate accurately. Secondly, the internal energy of the gas is only a tiny fraction of the total energy in the system (the vast majority of the energy resides in the radiation field), so that the vast majority of the energy is neglected in solving for the energy balance. The method presented in this paper, based on the /radiation energy balance/, addresses the bulk of the energy, does not depend on the heating/cooling rates, guarantees an accurate run of the bolometric luminosity over time while bringing the gas temperatures into consistence with the radiation field. We have implemented the method in the stellar atmosphere code PHOENIX and applied it to the classical W7 model. The results illustrate the importance of each of the four physical contributions to the energy balance as a function of time. The simulated spectra and light curves for W7 show good resemblance to the observations, which demonstrates what can be done using PHOENIX with the REB method.Comment: Accepted for publication in Ap

Emission from Pair-Instability Supernovae with Rotation

Pair Instability Supernovae have been suggested as candidates for some Super Luminous Supernovae, such as SN 2007bi, and as one of the dominant types of explosion occurring in the early Universe from massive, zero-metallicity Population III stars. The progenitors of such events can be rapidly rotating, therefore exhibiting different evolutionary properties due to the effects of rotationally-induced mixing and mass-loss. Proper identification of such events requires rigorous radiation hydrodynamics and radiative transfer calculations that capture not only the behavior of the light curve but also the spectral evolution of these events. We present radiation hydrodynamics and radiation transport calculations for 90-300 Msun rotating pair-instability supernovae covering both the shock break-out and late light curve phases. We also investigate cases of different initial metallicity and rotation rate to determine the impact of these parameters on the detailed spectral characteristics of these events. In agreement with recent results on non-rotating pair instability supernovae, we find that for a range of progenitor masses and rotation rates these events have intrinsically red colors in contradiction with observations of super-luminous supernovae. The spectroscopic properties of rotating pair instability supernovae are similar to those of non-rotating events with stripped hydrogen and helium envelopes. We find that the progenitor metallicity and rotation rate properties are erased after the explosion and cannot be identified in the resulting model spectra. It is the combined effects of pre-supernova mass-loss and the basic properties of the supernova ejecta such as mass, temperature and velocity that have the most direct impact in the model spectra of pair instability supernovae.Comment: 15 pages, 22 figures, submitted to Ap