  A hypermassive neutron star (HMNS) is a possible transient formed after the
merger of a neutron star binary. In the latest magnetohydrodynamic simulations
in full general relativity, we find that a magnetized HMNS undergoes `delayed'
collapse to a rotating black hole (BH) as a result of angular momentum
transport via magnetic braking and the magnetorotational instability. The
outcome is a BH surrounded by a massive, hot torus with a collimated magnetic
field. The torus accretes onto the BH at a quasi-steady accretion rate ~10
solar mass/s; the lifetime of the torus is ~10 ms. The torus has a temperature
\sim 10^{12} K, leading to copious neutrino-antineutrino thermal radiation.
Therefore, the collapse of an HMNS is a promising scenario for generating
short-duration gamma-ray bursts and an accompanying burst of gravitational
waves and neutrinos.
