2020RNAAS...4..207R

The dominant radioactive energy source powering SN Ia light curves is expected to switch from the decay of ⁵⁶Co to ⁵⁷Co at very late epochs. We use archival Hubble Space Telescope images of SN1992A obtained more than 900 days after explosion to constrain its cobalt isotopic abundance ratio and compare it to the well-studied event SN2011fe. We confirm the ⁵⁷Co/⁵⁶Co ratio for SN2011fe of 0.026 ± 0.004 found by Shappee et al., consistent with a “double degenerate” progenitor scenario. For SN1992A, we find a ratio of 0.034 ± 0.010, but the large uncertainty does not allow us to differentiate between progenitor models.