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The initial spins of pulsars are not well constrained by observations. Most millisecond pulsars are thought to be spun up by accretion, but accretion-induced collapse (AIC) of white dwarf is still a valid scenario. The pre-collapse white dwarf easily obtains a moderate amount of angular momentum by accreting material from its binary companion. Neutron stars formed via AIC can be rapidly rotating even if the original white dwarf core is not. After a brief dynamical phase, the nascent neutron star settles into an axisymmetric quasi-equilibrium state, but the gravitational radiation bar-mode instability drives the star to a nonaxisymmetric configuration on a dissipative (longer) timescale. The emitted quasi-periodic gravitational waves have a unique signature: the wave frequency sweeps downward from a few hundred Hertz to zero, while the wave amplitude increases from zero to a maximum and then decays back to zero. Such a wave signal could be detected by broad-band gravitational wave interferometers currently being constructed. Detection (or even non-detection) of the such gravitational wave can provide valuable constraint on the rotational properties of newly-formed neutron stars.
