  The currently-favored model for long-duration gamma-ray bursts (GRBs) invokes
explosions from the collapse of a massive star down to a black hole: either
directly or through fallback. Those GRBs forming via fallback will produce much
less radioactive nickel, and hence it has been argued (without any real
calculation) that these systems produce dim supernovae. These fallback
black-hole GRBs have been recently been argued as possible progenitors of a
newly discovered set of GRBs lacking any associated supernovae. Here we present
the first ever radiation-hydrodynamics calculations of the light-curves
produced in the hypernova explosion by a delayed-fallback gamma-ray burst. We
find that the bolometric light-curve is dominated by shock-deposited energy,
not the decay of radioactive elements. As such, observations of such bursts
actually probe the density in the progenitor wind more than it does the
production of radioactive nickel.
