Detection of Late-time Optical Emission from SN 1941C in NGC 4136

We report the detection of broad, high-velocity oxygen emission lines from the site of SN 1941C nearly eight decades after outburst, making it the oldest optically detected historical core-collapse supernova (CCSN) and one of the youngest CCSN remnants with a well determined age. In contrast to the strongly blueshifted emission line profiles observed for other late-time CCSNe thought to be due to internal dust extinction of far-side hemisphere of expanding ejecta, SN 1941C's spectrum exhibits stronger redshifted than blueshifted emissions of [O I] 6300, 6364 Å, [O II] 7319, 7330 Å, and [O III] 4959, 5007 Å. These oxygen emissions exhibit rest-frame expansion velocities from -2200 to $+4400\,\,\mathrm{km}\,{{\rm{s}}}^{-1}$ . No other significant broad line emissions were detected including Hα emission. We discuss possible causes for this unusual spectrum and compare SN 1941C's optical and X-ray luminosities to other evolved CCSNe.