  We study the evolution in axisymmetry of accretion disks formed
self-consistently through collapse of magnetized hypermassive neutron stars to
black holes. Such stars can arise following the merger of binary neutron stars.
They are differentially rotating, dynamically stable, and have rest masses
exceeding the mass limit for uniform rotation. However, hypermassive neutron
stars are secularly unstable to collapse due to MHD-driven angular momentum
transport. The rotating black hole which forms in this process is surrounded by
a hot, massive, magnetized torus and a magnetic field collimated along the spin
axis. This system is a candidate for the central engine of a short-hard
gamma-ray burst (GRB). Our code integrates the coupled Einstein-Maxwell-MHD
equations and is used to follow the collapse of magnetized hypermassive neutron
star models in full general relativity until the spacetime settles down to a
quasi-stationary state. We then employ the Cowling approximation, in which the
spacetime is frozen, to track the subsequent evolution of the disk. This
approximation allows us to greatly extend the disk evolutions and study the
resulting outflows, which may be relevant to the generation of a GRB. We find
that outflows are suppressed when a stiff equation of state is assumed for low
density disk material and are sensitive to the initial magnetic field
configuration.
