What Produced the Ultraluminous Supernova Remnant in NGC 6946?

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.

20 pages, 5 figures. To be published in The Astronomical Journal, March 2000

References in corpus (2)

• Detection of X-ray-Emitting Hypernova Remnants in M101
• ROSAT HRI and ASCA Observations of the Spiral Galaxy NGC 6946 and Its Northeast Complex of Luminous SNRs

Cited by in corpus (19)

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• Spectroscopy of Optical Counterparts of Ultraluminous X-ray Sources
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• A ULX microquasar in NGC 5408?
• The Long-Term Variability of the X-Ray Sources in NGC 6946 and NGC 4485/4490
• Revisiting the ultraluminous supersoft source in M101: an optically thick outflow model
• Chandra Observation of the X-Ray Source Population of NGC 6946
• Direct Detection of an Ultraluminous Ultraviolet Source
• A New, Larger Sample of Supernova Remnants in NGC 6946
• ROSAT HRI and ASCA Observations of the Spiral Galaxy NGC 6946 and Its Northeast Complex of Luminous SNRs
• Ultra-luminous X-ray Sources as Supercritical Accretion Disks: Spectral Energy Distributions
• Physical Structure and Nature of Supernova Remnants in M101
• Radio Continuum Imaging of the Spiral Galaxy NGC 4258
• Spitzer Observations of MF 16 Nebula and the associated Ultraluminous X-ray Source
• The Supernova Remnant Population of NGC6946 as Observed in [Fe II] 1.644 $\mu$m with HST
• Internal kinematics of giant H II regions in M101 with the Keck Cosmic Web Imager
• Narrow Lines in Type II Supernovae -- Probing the Circumstellar Nebulae of the Progenitors
• The Masses of Supernova Remnant Progenitors in NGC 6946
• The Optical Counterpart of an Ultraluminous X-ray Source NGC6946 ULX-1