Probing nuclear bubble structure via neutron star asteroseismology
Probing nuclear bubble structure via neutron star asteroseismology
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DOI：
10.1093/mnras/stw2575
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发表时间：
2016-09
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：
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作者：
H. Sotani;K. Iida;K. Oyamatsu
我们考虑的扭转振荡，被困在一层球形孔（泡）核结构，预计将发生在最深的区域的内壳的中子星星。由于这一层介于板状核的相和均匀核物质的外核之间，气泡相的扭转振荡可以与通常的地壳扭转振荡分开激发。我们发现，从本征模分析的各种模型的状态方程的均匀核物质，这种振荡的基本频率几乎是独立的对称核物质的不可压缩性，但强烈依赖于斜率参数的核对称性能量L$。虽然频率也对夹带效应敏感，即，在气泡外核子的哪一部分对振荡有贡献，通过固定这一部分，我们可以成功地将计算出的特定质量和半径的星星内气泡相扭转振荡的基频拟合为L的函数。通过比较由此产生的拟合公式的准周期振荡（QPOs）从软伽马中继器观察到的频率，我们发现，每个观察到的低频QPOs可以被确定为一个扭转振荡的气泡相或作为一个通常的地壳振荡，给出普遍接受的值$L$的所有恒星模型在这里考虑。
We consider torsional oscillations that are trapped in a layer of spherical-hole (bubble) nuclear structure, which is expected to occur in the deepest region of the inner crust of a neutron star. Because this layer intervenes between the phase of slab nuclei and the outer core of uniform nuclear matter, torsional oscillations in the bubble phase can be excited separately from usual crustal torsional oscillations. We find from eigenmode analyses for various models of the equation of state of uniform nuclear matter that the fundamental frequencies of such oscillations are almost independent of the incompressibility of symmetric nuclear matter, but strongly depend on the slope parameter of the nuclear symmetry energy $L$. Although the frequencies are also sensitive to the entrainment effect, i.e., what portion of nucleons outside bubbles contribute to the oscillations, by having such a portion fixed, we can successfully fit the calculated fundamental frequencies of torsional oscillations in the bubble phase inside a star of specific mass and radius as a function of $L$. By comparing the resultant fitting formula to the frequencies of quasi-periodic oscillations (QPOs) observed from the soft-gamma repeaters, we find that each of the observed low-frequency QPOs can be identified either as a torsional oscillation in the bubble phase or as a usual crustal oscillation, given generally accepted values of $L$ for all the stellar models considered here.