  Observational evidence suggests a link between long duration gamma ray bursts
(LGRBs) and Type Ic supernovae. Here, we propose a potential mechanism for Type
Ic supernovae in LGRB progenitors powered solely by accretion energy. We
present spherically-symmetric hydrodynamic simulations of the long-term
accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto
the central compact object, which we take to be a black hole. The simulations
were carried out with the adaptive mesh refinement code FLASH in one spatial
dimension and with rotation, an explicit shear viscosity, and convection in the
mixing length theory approximation. Once the accretion flow becomes
rotationally supported outside of the black hole, an accretion shock forms and
traverses the stellar envelope. Energy is carried from the central
geometrically thick accretion disk to the stellar envelope by convection.
Energy losses through neutrino emission and nuclear photodisintegration are
calculated but do not seem important following the rapid early drop of the
accretion rate following circularization. We find that the shock velocity,
energy, and unbound mass are sensitive to convective efficiency, effective
viscosity, and initial stellar angular momentum. Our simulations show that
given the appropriate combinations of stellar and physical parameters,
explosions with energies ~5x10^50 ergs, velocities 3000 km/s, and unbound
material masses >6 solar masses are possible in a rapidly rotating 16 solar
mass main sequence progenitor star. Further work is needed to constrain the
values of these parameters, to identify the likely outcomes in more plausible
and massive LRGB progenitors, and to explore nucleosynthetic implications.
