Galactic Positrons from Thermonuclear Supernovae

TL;DR

This study models positron escape from Type Ia supernovae using detailed simulations to evaluate their contribution to Galactic positrons, considering various explosion scenarios and magnetic field configurations.

Contribution

It provides the first comprehensive Monte Carlo simulation analysis of positron escape in diverse Type Ia supernova explosion models, including magnetic field effects.

Findings

Normal-bright SNe Ia dominate positron contribution.

Total SNe Ia contribution to Galactic positrons is less than 2%.

Magnetic field morphology influences positron escape fractions.

Abstract

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.