Detailed Multi-wavelength Study of the Late-Time Evolution of SN 1978K

SN 1978K is a remarkable Type IIn supernova that remains bright at Xray throughradio wavelengths 37 years after its explosion. While the radio flux droppedsteadily, the Xray and UV/optical fluxes remained constant for a decade. Ourrecent XMMNewton and Suzaku observations revealed these are now fading, butapparently with chromatic variations. Our millimeter detection makes this thefirst old extragalactic supernova to be detected in this band, apart from SN1987A. Only SN 1978K was detected in a search for warm dust in supernovae in thetransitional phase (age 10100 years). Here we request a 100 ksec XMMNewtonobservation as part of our detailed multiwavelength study of its evolution.This will serve as a pathfinder for younger Type IIn supernovae. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]