标题： 是什么产生了NGC 6946中的超亮超新星遗迹？ 显示英文标题

标题： What Produced the Ultraluminous Supernova Remnant in NGC 6946?

摘要： NGC 6946中的超亮超新星遗迹（SNR）是已知最亮的X射线SNR，大约比Cas A亮1000倍。 为了研究这一遗迹及其前身的性质，我们获得了高色散光学阶梯光谱。 阶梯光谱探测到了H-α、[N II]和[O III]线，并将这些线分解为来自未冲击物质的窄成分（FWHM ~20–40公里/秒）和来自冲击物质的宽成分（FWHM ~250公里/秒）。 窄成分和宽成分都具有异常高的[N II]/H-α比率，约为1。 利用阶梯观测、档案HST图像以及档案ROSAT X射线观测，我们得出结论，该SNR是由一颗正常超新星产生的，其前身是一颗大质量恒星，要么是WN星，要么是明亮的蓝变星。 遗迹的高亮度是由超新星喷发物进入由前身星创建的密集且富含氮的周围星云引起的。 显示英文摘要

摘要： 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.