Exploring the Supernova — Supernova Remnant Connection Through Late-Time Optical and X-ray Observations of SN 1996cr

SN 1996cr is a young, luminous supernova in the nearby galaxy of Circinus. When it was serendipitously discovered, it was classified as a Type IIn SN. Here we present low-dispersion Magellan IMACS spectra and CCD resolution Chandra X-ray spectra obtained ~ 20 years after core collapse. These new data show significant differences compared with previous observations. Optical spectra show broad, double-peaked emission lines of intermediate mass elements with expansion velocities < 4500 km/s, plus broad ± 2600 km/s hydrogen emission . Redshifted oxygen and sulfur emissions are considerably fainter than blueshifted emissions, suggestive of considerable internal dust extinction. The recent Chandra data suggest that the blast wave has recently broken free of a CSM shell which previously led to bright X-ray emission. Taken together, these new observations further confirm that SN 1996cr evolved inside of and interacted with a distant CSM shell similar to other late-interacting SNe such as 2014C or 2001em. We discuss SN 1996cr in the context of other interacting supernovae and its relation to young supernova remnants.