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.
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机译:NGC 6946中的超发光超新星残留(SNR)是X射线中已知的最亮的SNR,比Cas A的亮度约高1000倍。为探查这种残留物及其祖先的性质,我们获得了高色散的光学阶梯光谱。 echelle光谱检测到Hα,[N II]和[O III]谱线,并将这些谱线分解为不受震动的物质的窄(FWHM〜20–40 km s-1)分量和宽(FWHM〜250 km s-1)的分量)由震动的材料制成的组件。窄分量和宽分量都具有异常高的[N II] /Hα比,大约为1。使用echelle观测,哈勃太空望远镜的影像和ROSAT X射线档案的观测,我们得出结论,信噪比是由正常超新星产生的,祖先是一颗巨大的恒星,可以是WN恒星,也可以是发光的蓝色变星。残留物的高发光度是由超新星喷射膨胀成由祖先产生的致密,富氮的星状星云造成的。
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