A. Passamonti, K. Glampedakis
We study the damping of the gravitational radiation-driven f-mode instability
in ro- tating neutron stars by nonlinear bulk viscosity in the so-called
supra-thermal regime. In this regime the dissipative action of bulk viscosity
is known to be enhanced as a result of nonlinear contributions with respect to
the oscillation amplitude. Our anal- ysis of the f-mode instability is based on
a time-domain code that evolves linear perturbations of rapidly rotating
polytropic neutron star models. The extracted mode frequency and eigenfunctions
are subsequently used in standard energy integrals for the gravitational wave
growth and viscous damping. We find that nonlinear bulk vis- cosity has a
moderate impact on the size of the f-mode instability window, becoming an
important factor and saturating the mode's growth at a relatively large
oscillation amplitude. We show that a similar result holds for the damping of
the inertial r-mode instability by nonlinear bulk viscosity. In addition, we
show that the action of bulk viscosity can be significantly mitigated by the
presence of superfluidity in neutron star matter. Apart from revising the
f-mode's instability window we provide results on the mode's gravitational wave
detectability. Considering an f-mode-unstable neutron star located in the Virgo
cluster and assuming a mode amplitude at the level allowed by bulk viscosity,
we find that the emitted gravitational wave signal could be detectable by
advanced ground-based detectors such as Advanced LIGO/Virgo and the Einstein
Telescope.
View original:
http://arxiv.org/abs/1112.3931
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