Constraints on the nuclear equation of state and the neutron star structure from crustal torsional oscillations
Constraints on the nuclear equation of state and the neutron star structure from crustal torsional oscillations
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DOI：
10.1093/mnras/sty1755
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发表时间：
2018-07
影响因子：
4.8
通讯作者：
H. Sotani;K. Iida;K. Oyamatsu
中科院分区：
文献类型：
--
作者：
H. Sotani;K. Iida;K. Oyamatsu
我们系统地研究扭转剪切振荡的中子星星壳的新考虑到可能存在的相位的圆柱形核。在这项研究中，我们忽略了磁场的影响，在这种情况下，剪切振荡可以被磁相互作用阻尼。首先，通过识别低频准周期振荡（QPOs）中观察到的软伽马中继器（SGRs）的基本扭转振荡，我们约束的斜率参数的核对称能，$L$，合理的值的星星的质量$M$和半径$R$。同时，我们发现对于给定的$M$和$R$获得的扭转振荡的第一泛音可以很好地表示为新参数$\varsigma\equiv（K_0^4 L^5）^{1/9}$的函数，其中$K_0$是对称核物质的不可压缩性。假设在SGR 1806-20中观察到的500 Hz以上的QPO频率的最低值来自第一泛音，我们可以限制$\varsigma$的值。然后，对于每个中子星星模型，可以从观测到的低频QPO获得的$L$值通过上述对$\varsigma$的约束转换为$K_0$的最佳值。最后，它的一致性与允许值的$K_0$从经验巨磁共振导致中子星星模型具有相对较低的质量和大半径，这是定性类似的预测在早期的调查。这一结果表明，$L\simeq 58-73$兆电子伏，即使在圆柱形核的相位内的中子超流密度的不确定性是允许的。
We systematically examine torsional shear oscillations of neutron star crusts by newly taking into account the possible presence of the phase of cylindrical nuclei. In this study, we neglect an effect of magnetic fields, under which the shear oscillations can be damped by the magnetic interaction. First, by identifying the low frequency quasi-periodic oscillations (QPOs) observed in the soft-gamma repeaters (SGRs) as the fundamental torsional oscillations, we constrain the slope parameter of the nuclear symmetry energy, $L$, for reasonable values of the star's mass $M$ and radius $R$. Meanwhile, we find that the 1st overtone of torsional oscillations obtained for given $M$ and $R$ can be expressed well as a function of a new parameter $\varsigma\equiv (K_0^4 L^5)^{1/9}$, where $K_0$ is the incompressibility of symmetric nuclear matter. Assuming that the lowest of the QPO frequencies above 500 Hz observed in SGR 1806-20 comes from the 1st overtone, we can constrain the value of $\varsigma$. Then, for each neutron star model, such a value of $L$ as can be obtained from the observed low frequency QPOs translates to the optimal value of $K_0$ via the above constraint on $\varsigma$. Finally, its consistency with allowed values of $K_0$ from empirical giant monopole resonances leads to neutron star models with relatively low mass and large radius, which are qualitatively similar to the prediction in earlier investigations. This result suggests that $L\simeq 58-73$ MeV, even when uncertainties in the neutron superfluid density inside the phase of cylindrical nuclei are allowed for.