SN 1978K: An evolved supernova outside our Local Group detected at
  millimetre wavelengths
  Supernova 1978K is one of the oldest-known examples of the class of Type IIn
supernovae that show evidence for strong interaction between the blast wave and
a dense, pre-existing circumstellar medium. Here we report detections of SN
1978K at both 34 GHz and 94 GHz, making it only the third extragalactic
supernova (after SN 1987A and SN 1996cr) to be detected at late-times at these
frequencies. We find SN 1978K to be >400 times more luminous than SN 1987A at
millimetre wavelengths in spite of the roughly nine year difference in ages,
highlighting the risk in adopting SN 1987A as a template for the evolution of
core-collapse supernovae in general. Additionally, from new VLBI observations
at 8.4 GHz, we measure a deconvolved diameter for SN 1978K of ~5 milli-arcsec,
and a corresponding average expansion velocity of <1500 km/s. These
observations provide independent evidence of an extremely dense circumstellar
medium surrounding the progenitor star.
