Imprints of high-density nuclear symmetry energy on the crustal fraction of neutron star moment of inertia

Abstract

The density dependence of nuclear symmetry energy $E_{\rm sym}(\rho)$ remains the most uncertain aspect of the equation of state (EOS) of supradense neutron-rich nucleonic matter. Implications of observational crustal fraction of neutron star (NS) moment of inertia $\Delta I/I$ on the $E_{\rm sym}(\rho)$ are examined in the present work, utilizing an isospin-dependent parameterization of NS EOS. We find that symmetry energy parameters significantly influence the $\Delta I/I$, while the EOS of symmetric nuclear matter has a negligible effect. An increase in the slope $L$ and skewness $J_{\rm sym}$ of symmetry energy results in a larger $\Delta I/I$, whereas an increase in the curvature $K_{\rm sym}$ leads to a reduction in $\Delta I/I$. Additionally, we discuss the imprints of observational $\Delta I/I$ on the symmetry energy for NSs with masses of 1.0 M$_\odot$ or 1.4 M$_\odot$. Our results indicate that the $\Delta I/I$ has the potential to set a lower limit of symmetry energy at densities exceeding $3\rho_0$, particularly when $L$ is constrained to values less than $60$ MeV, thereby enhancing our understanding of supradense NS matter.