Galactic Positrons from Thermonuclear Supernovae

Type Ia Supernovae (SNe Ia) may originate from a wide variety of explosion scenarios and progenitor channels. They exhibit a factor of about 10 difference in brightness and, thus, a differentiation in the mass of 56Ni->56Co->56 Fe. We present a study on the fate of positrons within SNe Ia in order to evaluate their escape fractions and energy spectra. Our detailed Monte Carlo transport simulations for positrons and gamma-rays include both beta + decay of 56 Co and pair production. We simulate a wide variety of explosion scenarios, including the explosion of white dwarfs (WD) close to the Chandrasekhar mass, M(Ch), He-triggered explosions of sub-M Ch WDs, and dynamical mergers of two WDs. For each model, we study the influence of the size and morphology of the progenitor magnetic field between 1 and 1E13 G. Population synthesis based on the observed brightness distribution of SNe Ia was used to estimate the overall contributions to Galactic positrons due to escape from SN Ia. We find that this is dominated by normal-bright SNe Ia, where variations in the distribution of emitted positrons are small. We estimate a total SNe Ia contribution to the Galactic positrons of < 2% and, depending on the magnetic field morphology, less than 6...20% for M(Ch) and sub-M(Ch), respectively.
Comment: 16 pages, 9 figures, 5 tables