Physical Properties of the X-Ray–Luminous SN 1978K in NGC 1313 from Multiwavelength Observations

We update the light curves from the X-ray, optical, and radio bandpasseswhich we have assembled over the past decade, and present two observations inthe ultraviolet using the Hubble Space Telescope Faint Object Spectrograph. TheHRI X-ray light curve is constant within the errors over the entire observationperiod. This behavior is confirmed in the ASCA GIS data obtained in 1993 and1995. In the ultraviolet, we detected Ly-alpha, the [Ne IV] 2422/2424 Adoublet, the Mg II doublet at 2800 A, and a line at ~3190 A we attribute to HeI 3187. Only the Mg II and He I lines are detected at SN1978K's position. Theoptical light curve is formally constant within the errors, although a slightupward trend may be present. The radio light curve continues its steep decline. The longer time span of our radio observations compared to previous studiesshows that SN1978K is in the same class of highly X-ray and radio-luminoussupernovae as SN1986J and SN1988Z. The [Ne IV] emission is spatially distantfrom the location of SN1978K and originates in the pre-shocked matter. The MgII doublet flux ratio implies the quantity of line optical depth times densityof ~10^14 cm^-3 for its emission region. The emission site must lie in theshocked gas.Comment: 32 pages, 13 figs; LaTeX with AASTEXv5; paper accepted, scheduled for AJ, Dec 199