Nuclear symmetry energy and ther-mode instability of neutron stars
Physical Review C
We analyze the role of the symmetry energy slope parameter L on the r-mode instability of neutron stars. Our study is performed using both microscopic and phenomenological approaches of the nuclear equation of state. The microscopic ones include the Brueckner--Hartree--Fock approximation, the well known variational equation of state of Akmal, Pandharipande and Ravenhall, and a parametrization of recent Auxiliary Field Diffusion Monte Carlo calculations. For the phenomenological approaches, we
... e several Skyrme forces and relativisic mean field models. Our results show that the r-mode instability region is smaller for those models which give larger values of L. The reason is that both bulk (ξ) and shear (η) viscosities increase with L and, therefore, the damping of the mode is more efficient for the models with larger L. We show also that the dependence of both viscosities on L can be described at each density by simple power-laws of the type ξ=A_ξL^B_ξ and η=A_ηL^B_η. Using the measured spin frequency and the estimated core temperature of the pulsar in the low-mass X-ray binary 4U 1608-52, we conclude that observational data seem to favor values of L larger than ∼ 50 MeV if this object is assumed to be outside the instability region, its radius is in the range 11.5-12(11.5-13) km, and its mass 1.4M_(2M_). Outside this range it is not possible to draw any conclusion on L from this pulsar.