Evolving into a remnant: optical observations of SN 1978K at three decades

Abstract

We present new optical observations of the supernova SN 1978K, obtained in 2007 and 2014 with the Very Large Telescope. We discover that the supernova has not faded significantly, even more than three decades after its explosion. The spectrum exhibits numerous narrow (FWHM $\lesssim 600$ km s${}^{-1}$) emission lines, indicating that the supernova blastwave is persistently interacting with dense circumstellar material (CSM). Evolution of emission lines indicates that the supernova ejecta is slowly progressing through the reverse shock, and has not expanded past the outer edge of the circumstellar envelope. We demonstrate that the CSM is not likely to be spherically distributed, with mass of $\lesssim$ 1 M${}_{\odot }$. The progenitor mass loss rate is estimated as $\gtrsim 0.01$ M${}_{\odot }$ yr${}^{-1}$. The slowly fading late-time light curve and spectra show striking similarity with SN 1987A, indicating that a rate at which the CSM is being swept-up by the blastwave is gradually decaying and SN 1978K is undergoing similar evolution to become a remnant. Due to its proximity (4 Mpc), SN 1978K serves as the next best example of late-time supernova evolution after SN 1987A.

12 pages, 9 figures, accepted to MNRAS (minor changes from v1)

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Cited by in corpus (15)

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• Constraints on core-collapse supernova progenitors from explosion site integral field spectroscopy
• Three-dimensional distribution of ejecta in Supernova 1987A at 10 000 days
• Supernova Impostors and other Gap Transients
• Do Some AGN Lack X-ray Emission?
• Molecular gas at supernova local environments unveiled by EDGE
• Two Distinct-Absorption X-Ray Components from Type IIn Supernovae: Evidence for Asphericity in the Circumstellar Medium
• A systematic reclassification of type IIn supernovae
• MUSE spectroscopy of the ULX NGC 1313 X-1: a shock-ionised bubble, an X-ray photoionised nebula, and two supernova remnants
• The Impact of Progenitor Mass Loss on the Dynamical and Spectral Evolution of Supernova Remnants
• First Detection of X-Ray Line Emission from Type IIn Supernova 1978K with XMM-Newton's RGS
• SN 1978K: An evolved supernova outside our Local Group detected at millimetre wavelengths
• The X-ray Decay of the ultraluminous supernova SN 1978K in NGC 1313
• ALMA, ATCA, and Spitzer Observations of the Luminous Extragalactic Supernova SN 1978K
• Discovery of young, oxygen-rich supernova remnants in PHANGS-MUSE galaxies