Light-Curve Calculations of Supernovae from Fallback Gamma-Ray Bursts

Abstract

The currently favored model for long-duration gamma-ray bursts(GRBs) invokes explosions from the collapse of a massive star downto a black hole, either directly or through fallback. Those GRBsforming via fallback will produce much less radioactive nickel, andhence it has been argued (without any real calculation) that thesesystems produce dim supernovae. These fallback black hole GRBs haverecently been argued as possible progenitors of a newly discoveredset of GRBs lacking any associated supernovae. Here we present thefirst ever radiation-hydrodynamics calculations of the light curvesproduced in the hypernova explosion by a delayed-fallback gamma-rayburst. We find that the bolometric light curve is dominated byshock-deposited energy, not the decay of radioactive elements. Assuch, observations of such bursts actually probe the density in theprogenitor wind more than it does the production of radioactivenickel.