Deciphering the Explosion Mechanism of Type Ia Supernovae Using Their Remnants. II. A Deep Dive into Double Detonations with SNR 0509-67.5

Type Ia supernovae (SNe) occur when a white dwarf (WD) explodes via runaway thermonuclear burning. To date, major uncertainties remain regarding the nature of the explosion mechanism and its observable signatures. In this work, we study how the double-detonation explosion mechanism, or helium shell detonation in a sub-Chandrasekhar WD followed by core detonation, shapes SN remnants (SNRs) and encodes information about the WD progenitor. We evolve a suite of double-detonation SN models to the remnant phase, up to several centuries after the explosion, and measure the characteristic sizes of substructures formed in the SNR due to turbulent mixing. By comparing our models to high-resolution optical observations of the young Type Ia SNR 0509-67.5, we find that the size distribution of its small-scale substructures is consistent with the double-detonation explosion mechanism and further places constraints on the carbon–oxygen core mass and helium shell mass of the WD progenitor. The observed sizes of iron-dominated and sulfur-dominated substructures in SNR 0509–67.5 indicate a progenitor core mass and a shell mass of 1 M _⊙ and ≳0.05 M _⊙ , respectively.