  We study the secular evolution and gravitational wave signature of a
newly-formed, rapidly rotating neutron star. The neutron star may arise from
core collapse in a massive star or from the accretion-induced collapse of a
white dwarf. After a brief dynamical phase, the nascent neutron star settles
into an axisymmetric, secularly unstable equilibrium state. Gravitational
radiation drives the star to a nonaxisymmetric, stationary equilibrium
configuration via the bar-mode instability. 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.
  We also characterize two other types of gravitational wave signals that could
arise in principle from a rapidly rotating, secularly unstable neutron star: a
high-frequency ($f\go 1000$ Hz) wave which increases the pattern-speed of the
star, and a wave that actually increases the angular momentum of the star.

Astrophysics