An optical spectrum of SN 1978K (NGC 1313) in the range of 4000–7200 Å was obtained on 1992 October 22, i.e. 14.4 yr after the outburst. The spectrum is still dominated by the narrow (FWHM≤ 560 km s−1) Hα line having a luminosity 2.2 × 1038 erg s–1 (D = 3.7 Mpc, Av = 0.64 mag), 1.5–2 times lower than the values derived from published data for 1989 December and 1990 October. There is no evidence for a broad Hα component (HWZI~3000–10000 km s–1) with an upper limit of luminosity ~3×1036 erg s–1. We suggest that the optical emission of SN 1978K originates from radiative shock waves propagating in the dense (~4×106 cm–3) clouds of a circumstellar wind. The cloud shock waves are driven by the expanding low-mass (M≤2M⊙) supernova ejecta with the present radius ~(2–3) × 1017 cm. The mass of circumstellar material involved in the dynamical interaction is ≈1M⊙ and the corresponding mass-loss rate of pre-SN wind is ~2 × 10–4 M⊙ yr–1. The observed X-ray emission is attributed to the shock waves in the boundary layer of the same population of clouds. Alternatively, however, the X-ray emission might emanate from the shock waves in a different cloud population with a lower density.
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Чугай et al. (1995) studied this question.