Large sky surveys are finding new types of supernovae that are either much brighter (super-luminous), fainter (sub-luminous), or of shorter or longer duration than the standard types resulting either from thermonuclear runaway on a white dwarf star (Type Ia) or the core-collapse of a massive star (Types Ibc, II). The light we see from typical supernovae is either from the initial explosion energy, or more often the result of radioactive decay in the expanding supernova material. However, several of the rare events do not seem to be powered in this way, and so it is interesting to think about alternative sources of energy for powering the light we see from supernovae.
We have recently explored one possible scenario for producing unusual supernovae. Core-collapse explosions may not eject the entire massive star: some of it may turn around and "fall back." If this material falling back forms a disk around the remaining neutron star or black hole, it could provide a large amount of accretion energy to the supernova. We have numerically estimated the rate of material falling back over a range of explosions and progenitor stars. Assuming some fraction of the available accretion energy is injected into the expanding supernova ejecta, we calculate approximate light curves. The results are compared to observed rare supernovae, and used to make predictions for future observations.
References: Dexter, J. & Kasen, D., ApJ, submitted (arxiv:1210.7240)