Properties Of Rotating Neutron Star In Density-Dependent Relativistic Mean-Field Models

Equilibrium sequences were developed for rotating neutron stars in the relativistic mean-field interaction framework using four density-dependent equations of state (EOSs) for the neutron star matter. These sequences were constructed for the observed rotation frequencies of 25, 317, 346, 716 and 1122Hz. The bounds of sequences, the secular axisymmetric instability, static and Keplerian 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 according to this stability region, and the allowable range of these quantities was then determined for each model. According to the results, 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 346Hz, respectively. On the other hand, all the selected EOSs properly described the rotation of PSR J1748-244ad and PSR J1739-285 at a frequency of 716 and 1122Hz, respectively. The mass of these stars was, therefore, in the range of [0.68, 2.14]M circle dot and [1.67, 2.24]M circle dot, respectively. The polar, forward and backward redshifts, and the quadrupole moment were calculated in all the selected rotating frequencies and the Keplerian sequence. The results were consistent with observations. Confirming the mass of 1.5-1.0+0.4M circle dot for EXO 0748-676, our result, ZP approximate to 0.3, will be close to the observed value, and the EOSs used in this study properly describe this star. Interestingly, the extremum of Kerr parameter, polar, forward and backward redshifts in all models reached constant values of, a/M approximate to 0.7, Zp approximate to 0.8, Zeqf approximate to -0.3 and Zeqb approximate to 2.2, respectively. 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 = 1122Hz.