r-mode instability of neutron stars in low-mass X-ray binaries: effects of Fermi surface depletion and superfluidity of dense matter

Abstract

The nucleon-nucleon correlation between nucleons leads to the Fermi surface depletion measured by a $Z$-factor in momentum distribution of dense nuclear matter. The roles of the Fermi surface depletion effect ($Z$-factor effect) and its quenched neutron triplet superfluidity of nuclear matter in viscosity and hence in the gravitational-wave-driven $r$-mode instability of neutron stars (NSs) are investigated. The bulk viscosity is reduced by both the two effects, especially the superfluid effect at low temperatures which is also able to reduce the inferred core temperature of NSs. Intriguingly, due to the neutron superfluidity, the core temperature of the NSs in known low-mass X-ray binaries (LMXBs) are found to be clearly divided into two groups: high and low temperatures which correspond to NSs with short and long recurrence times for nuclear-powered bursts respectively. Yet, a large number of NSs in these LMXBs are still located in the $r$-mode instability region. If the density-dependent symmetry energy is stiff enough, the occurence of direct Urca process reduces the inferred core temperature by about one order of magnitude. Accordingly, the contradiction between the predictions and observations is alleviated to some extent, but some NSs are still located inside the unstable region.

12 pages, 5 figures

References in corpus (11)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter
• Probing Cold Dense Nuclear Matter
• Momentum sharing in imbalanced Fermi systems
• Tests of the nuclear equation of state and superfluid and superconducting gaps using the Cassiopeia A neutron star
• Shear viscosity in neutron star cores
• Density dependence of nuclear symmetry energy constrained by mean-field calculations
• Three-body force effect on nucleon momentum distributions in asymmetric nuclear matter within the framework of the extended BHF approach
• Density-dependent symmetry energy at subsaturation densities from nuclear mass differences
• X-ray bounds on the r-mode amplitude in millisecond pulsars
• Breakdown of the tensor component in the Skyrme energy density functional

Cited by in corpus (3)

• Role of nucleon-nucleon correlation in transport coefficients and gravitational-wave-driven $r$-mode instability of neutron stars
• Effects of nucleon-nucleon short-range correlation and symmetry energy on the evolution of newly born magnetars
• Evolution of Crab Pulsar: Magnetic Inclination Angle and Spin