1202.4731 (Isaac Vidana)

Nuclear symmetry energy and the r-mode instability of neutron stars    [PDF]

Isaac Vidana

We analyze the role of the symmetry energy slope parameter $L$ on the {\it r}-mode instability of neutron stars. Our study is performed using the microscopic Brueckner--Hartree--Fock approach of the nuclear equation of state, and several phenomenological Skyrme forces and relativistic mean field models. Our results show that the {\it r}-mode instability region is smaller for those models which give larger values of $L$. The reason is that both bulk ($\xi$) and shear ($\eta$) 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 $\xi=A_{\xi}L^{B_\xi}$ and $\eta=A_{\eta}L^{B_\eta}$. 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 seems to favor larger values of $L$ if the radius of this object is in the range $11.5-12$(10-12) km and its mass $1.4M_\odot$($2M_\odot$). Outside this range it is not possible to draw any conclusion on $L$ from this pulsar.

View original: http://arxiv.org/abs/1202.4731