Deriving Thermonuclear Supernova Properties from Gamma-Ray Line Measurements

Abstract

We illustrate methods for deriving properties of thermonuclear, or Type Ia, supernovae, including synthesized 56Ni mass, total ejecta mass, ejecta kinetic energy, and 56Ni distribution in velocity, from gamma-ray line observations. We simulate data from a small number of published SNe Ia models for a simple gamma-ray instrument, and measure their underlying properties from straightforward analyses. Assuming spherical symmetry and homologous expansion, we calculate exact line profiles for all 56Co and 56Ni lines at all times, requiring only the variation of mass density and 56Ni mass fraction with expansion velocity as input. By parameterizing these quantities, we iterate the parameters to fit the simulated data. We fit the full profiles of multiple lines, or we integrate over the lines and fit line fluxes only versus time. Line profile fits are more robust, but in either case, we can recover accurately the values of the aforementioned properties of the models simulated, given sufficient signal to noise in the lines. A future gamma-ray mission with line sensitivity approaching 10−6 photons cm−2 s−1 would measure these properties for many SNe Ia, and with unprecedented precision and accuracy for a few per year. Our analyses applied to the reported 56Co lines from SN 2014J favor a low 56Ni mass and low ejecta mass, relative to other estimates.