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What Produced the Ultraluminous Supernova Remnant in NGC 6946?

Bryan C. Dunne·Robert A. Gruendl·You-Hua Chu
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Abstract

The ultraluminous supernova remnant (SNR) in NGC 6946 is the brightest known SNR in X-rays, ~1000 times brighter than Cas A. To probe the nature of this remnant and its progenitor, we have obtained high-dispersion optical echelle spectra. The echelle spectra detect H-alpha, [N II], and [O III] lines, and resolve these lines into a narrow (FWHM ~20--40 km/s) component from un-shocked material and a broad (FWHM ~250 km/s) component from shocked material. Both narrow and broad components have unusually high [N II]/H-alpha ratios, ~1. Using the echelle observation, archival HST images, and archival ROSAT X-ray observations, we conclude that the SNR was produced by a normal supernova, whose progenitor was a massive star, either a WN star or a luminous blue variable. The high luminosity of the remnant is caused by the supernova ejecta expanding into a dense, nitrogen-rich circumstellar nebula created by the progenitor.

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Bryan C. Dunne, Robert A. Gruendl, You-Hua Chu. 1999-12-01. What Produced the Ultraluminous Supernova Remnant in NGC 6946?. https://doi.org/10.1086/301264

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