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

TL;DR

This paper reports the detection of broad oxygen emission lines from SN 1941C, making it the oldest optically observed core-collapse supernova remnant, with unique redshifted emission profiles suggesting unusual ejecta dynamics.

Contribution

It presents the first detection of late-time optical emission from SN 1941C, revealing unusual spectral features that challenge typical dust extinction models for supernova remnants.

Findings

Detected broad oxygen emission lines 80 years post-explosion

SN 1941C shows stronger redshifted emissions unlike other CCSNe

Oxygen emission velocities range from -2200 to +4400 km/s

Abstract

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 core-collapse supernova/youngest core-collapse supernova remnant with a well determined age. In contrast to the strongly blueshifted emission line profiles observed for all other late-time CCSNe thought to be due to dust extinction of rear hemisphere ejecta, SN 1941C's spectrum exhibits stronger redshifted than blueshifted emissions of [O I] 6300, 6364 A, [O II] 7319, 7330 A, and [O III] 4959, 5007 A. The oxygen emissions exhibit rest frame expansion velocities of -2200 to +4400 km/s. No other significant broad line emissions were detected including Halpha emission. We discuss possible causes for this unusual spectrum and compare SN 1941C's optical and X-ray luminosities to other evolved CCSNe.