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When a Type Ia supernova (SN Ia) progenitor first ignites carbon in its core,it undergoes ${\sim} \,10^{3}-10^{4} \,$yr of convective burning prior to theonset of thermonuclear runaway. This carbon simmering phase is important forsetting the thermal profile and composition of the white dwarf. Using the\texttt{MESA} stellar evolution code, we follow this convective burning andexamine the production of neutron-rich isotopes. The neutron content of the SNfuel has important consequences for the ensuing nucleosynthesis, and, inparticular, for the production of secondary Fe-peak nuclei like Mn and stableNi. These elements have been observed in the X-ray spectra of SN remnants likeTycho, Kepler, and 3C 397, and their yields can provide valuable insights intothe physics of SNe Ia and the properties of their progenitors. We find thatweak reactions during simmering can at most generate a neutron excess of${\approx} \, 3 \times 10^{-4}$. This is ${\approx} \, 8 \times 10^{-4}$ lowerthan that found in previous studies that do not take the full density andtemperature profile of the simmering region into account. Our results implythat the progenitor metallicity is the main contributor to the neutron excessin SN Ia fuel for $Z \gtrsim 1/3 \, Z_{\odot}$. Alternatively, at lowermetallicities, this neutron excess provides a floor that should be present inany centrally-ignited SN~Ia scenario.

Neutronization During Carbon Simmering In Type Ia Supernova Progenitors