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首页> 外文期刊>The Astrophysical journal >NONRADIAL OSCILLATIONS IN NEUTRON STAR OCEANS: A SOURCE OF QUASI-PERIODIC X-RAY OSCILLATIONS?
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NONRADIAL OSCILLATIONS IN NEUTRON STAR OCEANS: A SOURCE OF QUASI-PERIODIC X-RAY OSCILLATIONS?

机译：中子星海洋的非径向振荡：准周期X射线振荡的来源吗？

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The detection of quasi-periodic oscillations in the brightest X-ray sources has opened up a new window on the properties of accreting neutron stars. All six of the highest accretion rate (M approx> 10~(-9) solar mass yr~(-1)) sources have exhibited oscillations in the 5-7 Hz range. We explore the possibility that the underlying clock for this feature is a low l nonradial oscillation in the neutron star "ocean." The composition of the ocean at densities approx> 10~7 g cm~(-3) depends on how the accreted hydrogen and helium is burned to heavier elements, which in turn depends on the accretion rate. In particular, the high accretion rate sources develop deep, massive oceans of light elements (C, O, Ne, Mg, ...). In contrast, low accretion rate sources burn the accreted matter to iron group elements at low densities through type I X-ray bursts. The stronger Coulomb forces in the iron plasma leads to crystallization just beneath the burning region, and therefore lower accretion rate sources have much shallower, less massive oceans than the higher accretion rate sources. Our adiabatic nonradial mode calculations show that the deep ocean of light elements supports g-modes (basically shallow water waves) with frequencies (for l = 1) that are a compelling match to the observed ≈5-7 Hz quasi-periodic X-ray oscillations. In addition, these modes can contain up to 10~(37)-10~(38) ergs of energy and still be in the linear regime at the density where the frequency is set. The successful identification of a few nonradial modes with their observed frequencies would yield new information about the thermal and compositional makeup of the neutron star at densities in excess of 10~9 g cm~(-3). Our initial results are in the limit of slow rotation (i.e., P_s approx> 1/6 s) and weak magnetic fields (B approx< 10~(11) G), and we mention the differences rapid rotation might make. We also emphasize the promise afforded by "oceanography" of accreting neutron stars with the X-Ray Timing Explorer and USA satellites.
机译：在最亮的X射线源中准周期振荡的检测为积聚中子星的性质开辟了新窗口。所有六个最大吸积率源（M大约> 10〜（-9）太阳质量yr〜（-1））都在5-7 Hz范围内出现振荡。我们探索了该特征的潜在时钟是中子星“海洋”中低l非径向振荡的可能性。密度大约为10〜7 g cm〜（-3）的海洋成分取决于所吸收的氢和氦如何燃烧成更重的元素，进而取决于其吸收速率。特别是，高吸积率源会形成大量的轻元素（C，O，Ne，Mg等）海洋。相反，低吸积率源通过I型X射线爆发将吸积物以低密度燃烧成铁族元素。铁等离子体中较强的库仑力会导致在燃烧区域正下方的结晶，因此，与高吸积率源相比，低吸积率源具有更浅，更小的海洋。我们的绝热非径向模式计算表明，深层轻元素支持的g模式（基本为浅水波）的频率（对于l = 1）与观察到的≈5-7Hz准周期X射线非常匹配振荡。此外，这些模式最多可以包含10〜（37）-10〜（38）erg的能量，并且在设定频率的密度下仍处于线性状态。成功地识别几种非辐射模式及其观测频率，将产生有关密度超过10〜9 g cm〜（-3）的中子星热和组成组成的新信息。我们的初始结果是在慢速旋转（即P_s大约> 1/6 s）和弱磁场（B大约<10〜（11）G）的极限内，我们提到了快速旋转可能会产生的差异。我们还强调“海洋学”所提供的承诺，即利用X射线定时探测器和美国卫星吸收中子星。

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