Physical properties of the X-ray-luminous SN1978K in NGC 1313 from multiwavelength observations

We update the light curves from the X-ray, optical, and radio bandpasses wh ich we have assembled over the past decade and present two observations in the ultraviolet using the Hubble Space Telescope Faint Object Spectrograph. The HRI X-ray light curve is constant within the errors over the entire ob servation period. This behavior is confirmed in the ASCA GIS data obtained in 1993 and 1995. In the ultraviolet, we detected Ly alpha, the [Ne IV] 242 2/2424 Angstrom doublet, the Mg II. doublet at 2800 Angstrom, and a line at approximately 3190 Angstrom that we attribute to He I 3187. Only the Mg II and He I lines are detected at SN 1978K's position. The optical light curv e is formally constant within the errors, although a slight upward trend ma y be present. The radio light curve continues its steep decline. The longer time span of our radio observations compared to previous studies shows tha t SN 1978K is in the same class of highly X-ray and radio-luminous supernov ae as SN 1986J and SN 1988Z. The [Ne IV] emission is spatially distant from the location of SN 1978K and originates in the preshocked matter. The Mg I I doublet flux ratio implies the quantity of line optical depth times densi ty of approximately 10(14) cm(-3) for its emission region. The emission sit e must lie in the shocked gas.