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C. K. Lacey (NRL/NRC), K. W. Weiler (NRL), S. D. Van Dyk (IPAC/Caltech), R. A. Sramek (NRAO)
Long term monitoring of radio supernovae (RSNe) with the Very Large Array (VLA) has resulted in several RSNe with radio light curves at multiple frequencies that span at least a decade in time. As an RSN expands into the circumstellar medium (CSM), it becomes a probe into the properties of the CSM and stages of the stellar evolution prior to the explosion. A model of the radio emission has been used to successfully explain the global properties of the radio light curves observed, but significant departures from the predicted radio light curves have been found as the RSNe age. These deviations are thought to indicate changes in the CSM and are found to occur on rapid time scales (few thousand years) indicating rapid presupernova evolution of the progenitor stellar systems. The radio light curves of SN 1988Z and SN 1981K are presented and analyzed. Comparisons are drawn of SN 1988Z with SN 1980K, for which the radio light curve dropped precipitously, and SN 1981K with SN 1979C, for which the radio light curve has stopped declining in the predicted manner and, perhaps, even started increasing. The behavior of these four RSNe suggest at least two different radio evolution scenarios exist for RSNe: those whose flux densities suddenly decline below previous evolutionary tracks and those whose flux densities slowly increase above previous evolutionary tracks. Interpretation of these two phenomena in terms of presupernova mass loss histories will be discussed.
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