SIMBAD references

The radius R_1.4 of neutron stars (NSs) with a mass of 1.4 M_☉ has been extracted consistently in many recent studies in the literature. Using representative R_1.4 data, we infer high-density nuclear symmetry energy E_sym(ρ) and the associated nucleon specific energy E₀(ρ) in symmetric nuclear matter (SNM) within a Bayesian statistical approach using an explicitly isospin-dependent parametric equation of state (EOS) for nucleonic matter. We found the following. (1) The available astrophysical data can already significantly improve our current knowledge about the EOS in the density range of ρ₀ - 2.5ρ₀. In particular, the symmetry energy at twice the saturation density ρ₀ of nuclear matter is determined to be E_sym(2ρ₀)=39.2_–8.2^+12.1 MeV at a 68% confidence level. (2) A precise measurement of R_1.4 alone with a 4% 1σ statistical error but no systematic error will not greatly improve the constraints on the EOS of dense neutron-rich nucleonic matter compared to what we extracted from using the available radius data. (3) The R_1.4 radius data and other general conditions, such as the observed NS maximum mass and causality condition, introduce strong correlations for the high-order EOS parameters. Consequently, the high-density behavior of E_sym(ρ) inferred depends strongly on how the high-density SNM EOS E₀(ρ) is parameterized, and vice versa. (4) The value of the observed maximum NS mass and whether it is used as a sharp cutoff for the minimum maximum mass or through a Gaussian distribution significantly affects the lower boundaries of both E₀(ρ) and E_sym(ρ) only at densities higher than about 2.5ρ₀.