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 bandpasses which 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 observation period. This behavior is confirmed in the ASCA GIS data obtained in 1993 and 1995. In the ultraviolet, we detected Ly-α, the [Ne IV] 2422/2424 Å doublet, the Mg II doublet at 2800 Å, and a line at ∼3190 Å we attribute to He I 3187. Only the Mg II and He I lines are detected at SN1978K’s position. The optical light curve is formally constant within the errors, although a slight upward trend may be present. The radio light curve continues its steep decline. The longer time span of our radio observations compared to previous studies shows that SN1978K is in the same class of highly X-ray and radio-luminous supernovae as SN1986J and SN1988Z. The [Ne IV] emission is spatially distant from the location of SN1978K and originates in the pre-shocked matter. The Mg II doublet flux ratio implies the quantity of line optical depth times density of ∼10 cm for its emission region. The emission site must lie in the shocked gas. Subject headings: stars: supernovae: individual: SN1978K High Energy Astrophysics Division, Smithsonian Astrophysical Observatory, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 Joint Astronomy Center, 660 N. A’Ohoku Place, Hilo, HI 96720 Australia Telescope National Facility, CSIRO, P.O. Box 76, Epping, NSW 2121, Australia X-ray Astrophysics Group, Laboratory for High Energy Astrophysics, NASA-GSFC, Greenbelt, MD 20771 National Research Council Fellow Mount Stromlo and Siding Spring Observatories, Australian National University, Weston Creek P. O., ACT 2611, Australia Astrophysics Dept., School of Physics A29, University of Sydney, Sydney NSW 2006, Australia Based upon (i) archival ASCA observations obtained from the High Energy Astrophysics Science Archive Research Center On-line Service, which is provided by NASAGoddard Space Flight Center, (ii) ROSAT HRI PI observations, (iii) observations with the NASA/ESA Hubble Space Telescope (Faint Object Spectrograph), obtained at the Space Telescope Science Institute, which is operated by Associated Universities for Research in Astronomy, Inc.,