中子星的磁弹性振荡：探索不同的磁场位形
Magneto-elastic oscillations of neutron stars: exploring different magnetic field configurations
摘要：
我们研究了高磁化中子星（磁星）的磁弹性振荡，它被提出来解释软γ射线中继器（SGR）巨耀斑衰变尾部出现的准周期振荡（QPO）。我们通过调查各种磁场配置，计算在每种情况下的Alfvén谱，并进行磁弹性模拟选定数量的模型扩展以前的研究。通过识别观测到的28 Hz（SGR 1900+14）和30 Hz（SGR 1806-20）频率与基本Alfvén QPO，我们估计所需的表面磁场强度。对于所研究的磁场配置（类偶极向场，具有类偶极向分量的混合环向-极向场和限制在靠近恒星内部的场线区域的环向场，以及具有额外的类四极向分量的极向场）估计的偶极自旋下降磁场在8 × 10^14 G和4 × 10^15 G之间，与产生巨大耀斑的SGR源的自旋下降估计大体一致。许多模型都表现出丰富的阿尔文连续统，揭示了可以产生QPO的新转折点。这使得人们可以解释大多数观察到的QPO频率与磁弹性QPO。特别是，我们构造了一个可能的配置，在光谱中的两个转折点，可以解释所有观察到的QPO的SGR 1900+14。最后，我们发现，磁场配置完全局限于地壳（如果核心被假定为I型超导体）是不赞成的，由于难以解释的最低观测QPO频率（f<30 Hz）。
英文摘要：
We study magneto-elastic oscillations of highly magnetized neutron stars (magnetars) which have been proposed as an explanation for the quasi-periodic oscillations (QPOs) appearing in the decaying tail of the giant flares of soft gamma-ray repeaters (SGRs). We extend previous studies by investigating various magnetic field configurations, computing the Alfvén spectrum in each case and performing magneto-elastic simulations for a selected number of models. By identifying the observed frequencies of 28 Hz (SGR 1900+14) and 30 Hz (SGR 1806-20) with the fundamental Alfvén QPOs, we estimate the required surface magnetic field strength. For the magnetic field configurations investigated (dipole-like poloidal, mixed toroidal-poloidal with a dipole-like poloidal component and a toroidal field confined to the region of field lines closing inside the star, and for poloidal fields with an additional quadrupole-like component) the estimated dipole spin-down magnetic fields are between 8x10^14 G and 4x10^15 G, in broad agreement with spin-down estimates for the SGR sources producing giant flares. A number of these models exhibit a rich Alfvén continuum revealing new turning points which can produce QPOs. This allows one to explain most of the observed QPO frequencies as associated with magneto-elastic QPOs. In particular, we construct a possible configuration with two turning points in the spectrum which can explain all observed QPOs of SGR 1900+14. Finally, we find that magnetic field configurations which are entirely confined in the crust (if the core is assumed to be a type I superconductor) are not favoured, due to difficulties in explaining the lowest observed QPO frequencies (f<30 Hz).
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