Properties of Rotating Neutron Star in Density-dependent Relativistic Mean-field Models

TL;DR

This study models rotating neutron stars using density-dependent relativistic mean-field equations of state, analyzing stability, redshifts, and quadrupole moments across observed rotation frequencies, and compares results with observational data.

Contribution

It introduces detailed equilibrium sequences for rotating neutron stars with multiple EOSs, highlighting their ability to describe observed pulsars and identifying universal behaviors of key parameters.

Findings

Certain EOSs fail to describe low-frequency pulsars.

All EOSs accurately model high-frequency pulsars at 716 and 1122 Hz.

Redshifts and Kerr parameter reach EOS-independent constant values.

Abstract

Equilibrium sequences were developed for rotating NS in the relativistic mean-field interaction framework using four density-dependent equations of state for the NS matter. These sequences were constructed for the observed rotation frequencies of 25, 317, 346, 716, and 1122 Hz. The bounds of sequences were calculated in each model to determine the stability region. The gravitational mass, quadrupole moment, polar, forward and backward redshifts, and Kerr parameter were calculated. DDF and DD-ME$\delta$ were unable to properly describe the low-frequency neutron stars, PSR J0348+432, PSR J1614-2230 , and PSR J0740+6620 rotate at a frequency of 25, 317, and 346 Hz, respectively. All the selected EOSs properly described the rotation of PSR J1748-244ad, and PSR J1739-285 at a frequency of 716 and 1122 Hz, respectively. The mass of these stars was in the range of [0.68, 2.14]M$_{\odot}$ and [1.67, 2.24]M$_{\odot}$, respectively. The polar, forward and backward redshifts, and the quadrupole moment were calculated in all selected rotating frequencies and the Keplerian sequence. The results were consistent with observations. Confirming the mass of $1.5^{+0.4}_{-1.0}M_{\odot}$ for EXO 0748-676, our result will be close to the observed value, and the EOSs used in this study properly describe this star. The extremum of Kerr parameter, polar, forward and backward redshifts in all models reached constant values of, a/M$\approx$ 0.7, Z$_{p}\approx$ 0.8, Z$_{eq}^{f}\approx$ -0.3 and Z$_{eq}^{b}\approx$ 2.2. These behaviors of redshifts and Kerr parameter are approximately independent of EOS. The observed behaviors must evaluate by other EOSs to find universal relations for these quantities. Also, a limit value was found for each of these parameters. In this case where these parameters are greater than the limit value, the star can rotate at a frequency equal to or greater than $\nu$= 1122 Hz.