New Perspectives on Type Ic Supernovae

The Type Ic supernovae are probably “nearly-nude” core collapse events. They are thus of special interest in terms of their evolutionary origin, but also as the source of potential clues to the explosion process that may not be obtained from other supernovae. Study of Type Ic shows that they are distinct from Type Ia, even those of the dimmer, redder variety. Type Ic also suggest that the historical classification scheme based on spectra cannot encompass the physical features of these and closely related events. The Type Ic probably all have a very small outer layer of helium, but not enough to make them merely a version of Type Ib. They probably require another evolutionary channel. Similar spectra near maximum light belie a variety of late-time light curve behavior. Some events classified as Type Ic, eg SN 1962L, 1983V, 1990B, and 1990U, follow a relatively slow evolution after maximum light, decaying ∼3.0 magnitudes in V during the first 150 days after maximum. These events seem to belong to a general category that includes SN 1993J and the Type Ib SN 19983N. Their light curves decline more rapidly than the expected late-time 56Co decay with full trapping, but less rapidly than Type Ia. The late time light curve of these events seems to be independent of the velocity of the ejecta and hence implies the trapping of γ-rays in a manner that is independent of the mass that participates in the homologous expansion. Other Type Ic, SNe 1983I, 1987M, and 1994I, show steeper decline than even Type Ia. 2 A. CLOCCHIATTI AND J. C. WHEELER