磁星外场拓扑。I.轴对称场
Topology of magnetars external field. I. Axially symmetric fields
摘要：
越来越多的理论和观测证据表明，磁星的外部磁场可能包含一个环向分量，可能与极向分量的量级相同。这种“扭曲的磁层”被沿着闭合场线流动的电流穿过，该闭合场线可以通过共振回旋散射（RCS）与软热光子有效地相互作用。实际上，RCS谱模型在解释候选磁星、软γ射线中继器（SGR）和异常X射线源（AXP）的持续~1-10 keV辐射方面是相当成功的。此外，有人提出，在存在高度相对论性电子的情况下，相同的过程可以引起所观察到的硬X射线谱尾延伸到~200 keV。到目前为止，光谱计算一直局限于全球扭曲的偶极磁层的情况下，虽然有迹象表明，扭曲可能只限于磁层的一部分，和/或大规模的领域是更复杂的比一个简单的偶极子。本文研究了超磁化中子星的多极无力磁层。本文首先讨论了Grad-Schluter-Shafranov方程多极解的一般生成方法，并详细分析了偶极、四极和八极场。这些多极，全球扭曲领域的光谱和光变曲线，然后使用蒙特卡罗代码计算和比较与那些一个纯粹的偶极配置。最后，相位分辨光谱和能量依赖的光变曲线得到了一个简单的模型的局部剪切场面临的积分观测的AXP 1 RXS J1708-4009和4U 0142+61。结果支持的图片，在这两个来源的领域是不是全球扭曲。
英文摘要：
There is an increasing theoretical and observational evidence that the external magnetic field of magnetars may contain a toroidal component, likely of the same order of the poloidal one. Such "twisted magnetospheres" are threaded by currents flowing along the closed field lines which can efficiently interact with soft thermal photons via resonant cyclotron scatterings (RCS). Actually, RCS spectral models proved quite successful in explaining the persistent ~1-10 keV emission from the magnetar candidates, the soft gamma-ray repeaters (SGRs) and the anomalous X-ray pulsars (AXPs). Moreover, it has been proposed that, in presence of highly relativistic electrons, the same process can give rise to the observed hard X-ray spectral tails extending up to ~200 keV. Spectral calculations have been restricted up to now to the case of a globally twisted dipolar magnetosphere, although there are indications that the twist may be confined only to a portion of the magnetosphere, and/or that the large scale field is more complex than a simple dipole. In this paper we investigate multipolar, force-free magnetospheres of ultra-magnetized neutron stars. We first discuss a general method to generate multipolar solutions of the Grad- Schluter-Shafranov equation, and analyze in detail dipolar, quadrupolar and octupolar fields. The spectra and lightcurves for these multipolar, globally twisted fields are then computed using a Monte Carlo code and compared with those of a purely dipolar configuration. Finally the phase-resolved spectra and energy-dependent lightcurves obtained with a simple model of a locally sheared field are confronted with the INTEGRAL observations of the AXPs 1RXS J1708-4009 and 4U 0142+61. Results support a picture in which the field in these two sources is not globally twisted.
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