The nebular spectra of SN 2023ixf: A lower mass, partially stripped progenitor may be the result of binary interaction

SN 2023ixf is one of the brightest Core Collapse Supernovae of the 21st century and offers a rare opportunity to investigate the late stage of a Supernova through nebular phase spectroscopy. We present four nebular phase spectra from day +291 to +413 after explosion. This is supplemented with high cadence early phase spectroscopic observations and photometry covering the first 500 days to investigate explosion parameters. The narrow and blue-shifted nebular Oxygen emission lines are used to infer an ejected Oxygen mass of <0.65M⊙, consistent with models of a relatively low mass (MZAMS < 15M⊙) progenitor. An energy of 0.3 to 1.4 × 1051 erg and a light curve powered by an initial 56Ni mass of 0.049 ± 0.005M⊙ appear consistent with a relatively standard Type II explosion, while an incomplete γ-ray trapping (with timescale of 240 ± 4 days) suggests a lower ejecta mass. Assuming a typical explosion, the broad Hydrogen and Calcium profiles suggest a common origin within a lower mass, partially stripped envelope. Hydrogen emission broadens with time, indicating contribution from an additional power source at an extended distance; while the emergence of high velocity (∼6,000 km s−1) Hydrogen emission features (beginning around day +200) may be explained by Shock Interaction with a dense Hydrogen-rich region located at ∼1.5 × 1016cm. Such envelope mass loss for a low mass progenitor may be explained through theoretical models of Binary interaction.