ALMA, ATCA, and Spitzer observations of the luminous extragalactic supernova SN 1978K

I. A. Smith, S. D. Ryder, R. Kotak, E. C. Kool, S. K. Randall

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    Only three extragalactic supernovae have been detected at late times at millimeter wavelengths: SN 1987A, SN 1978K, and SN 1996cr. SN 1978K is a remarkably luminous Type IIn supernova that remains bright at all wavelengths 40 years after its explosion. Here, we present Atacama Large Millimeter/submillimeter Array (ALMA) observations taken in 2016 using Bands 3, 4, 6, and 7 that show a steepening in the spectrum. An absorbed single power-law model broadly fits all of the radio and millimeter observations, but would require significant chromatic variability. Alternatively, a broken power law fits the radio-millimeter spectrum; this can be explained using an ultra-relativistic spherical blast wave in a wind scaling with a cooling break, as in a gamma-ray burst afterglow. Using updated Australia Telescope Compact Array light curves, we show that the non-thermal radio continuum continues to decay as t -1.53; in the fireball model, this independently defines the power-law indices found in the radio-millimeter spectrum. Supernovae such as SN 1978K might be important contributors to the universal dust budget: only SN 1978K was detected in a search for warm dust in supernovae in the transitional phase (age 10-100 yr). Using Spitzer Space Telescope observations, we show that at least some of this dust emission has been decaying rapidly as t -2.45 over the past decade, suggesting it is being destroyed. Depending on the modeling of the synchrotron emission, the ALMA observations suggest there may be emission from a cold dust component.

    Original languageEnglish
    Article number59
    Pages (from-to)1-10
    Number of pages10
    JournalAstrophysical Journal
    Issue number2
    Publication statusPublished - 10 Jan 2019

    Bibliographical note

    Copyright 2019 The American Astronomical Society. First published in the Astrophysical journal, 870(2), 59, 2019, published by IOP Publishing. The original publication is available at Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


    • galaxies: individual (NGC 1313)
    • gamma-ray burst: general
    • supernovae: general
    • supernovae: individual (SN 1978K)


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