What produced the ultraluminous supernova remnant in NGC 6946?

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The ultraluminous supernova remnant (SNR) in NGC 6946 is the brightest known SNR in X-rays, about 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 Hα, [N II], and [O III] lines and resolve these lines into a narrow (FWHM ∼20-40 km s-1) component from unshocked material and a broad (FWHM ∼250 km s-1) component from shocked material. Both narrow and broad components have unusually high [N II]/Hα ratios, about 1. Using the echelle observation, archival Hubble Space Telescope 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.

Original languageEnglish (US)
Pages (from-to)1172-1179
Number of pages8
JournalAstronomical Journal
Issue number3
StatePublished - Mar 2000


  • Galaxies: individual (NGC 6946)
  • H II regions
  • ISM: bubbles
  • Stars: Wolf-Rayet
  • Supernova remnants

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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