  A weakly magnetized ($\sim 10^7$G) neutron star, slowly spun up by accretion
in an X-ray binary, crosses the instability boundary for r-mode instability at
P=1--2 msec. The amplitude of the oscillation, which initially increases only
at the spinup time scale, is secularly unstable due to the negative temperature
dependence of the viscosity in neutron star matter, and diverges after a few
hundred years. Angular momentum loss by the gravitational wave causes strong
differential rotation, in which the magnetic field is wound up to $10^{17}$G on
a time scale of a few months. When this field becomes unstable to buoyancy
instability, a surface field strength of a few $10^{16}$G is produced on a time
scale of seconds, which then powers a GRB with energies of $\sim 1-8\times
10^{51}$ and duration of 1--100 sec.
