Evolving into a remnant: optical observations of SN 1978K at three
  decades
  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 $\lesssim600$ 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.
