Gourgouliatos Konstantinos N, Wood Toby S, Hollerbach Rainer
Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, United Kingdom;
School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom.
Proc Natl Acad Sci U S A. 2016 Apr 12;113(15):3944-9. doi: 10.1073/pnas.1522363113. Epub 2016 Mar 28.
Current models of magnetars require extremely strong magnetic fields to explain their observed quiescent and bursting emission, implying that the field strength within the star's outer crust is orders of magnitude larger than the dipole component inferred from spin-down measurements. This presents a serious challenge to theories of magnetic field generation in a proto-neutron star. Here, we present detailed modeling of the evolution of the magnetic field in the crust of a neutron star through 3D simulations. We find that, in the plausible scenario of equipartition of energy between global-scale poloidal and toroidal magnetic components, magnetic instabilities transfer energy to nonaxisymmetric, kilometer-sized magnetic features, in which the local field strength can greatly exceed that of the global-scale field. These intense small-scale magnetic features can induce high-energy bursts through local crust yielding, and the localized enhancement of Ohmic heating can power the star's persistent emission. Thus, the observed diversity in magnetar behavior can be explained with mixed poloidal-toroidal fields of comparable energies.
目前的磁星模型需要极强的磁场来解释其观测到的宁静和爆发性辐射，这意味着恒星外壳内的场强比从自转减慢测量推断出的偶极分量大几个数量级。这对原中子星磁场产生理论提出了严峻挑战。在此，我们通过三维模拟对中子星外壳磁场演化进行了详细建模。我们发现，在全球尺度的极向和环向磁分量能量均分的合理情形下，磁不稳定性将能量转移到非轴对称的、千米大小的磁特征中，其中局部场强可大大超过全球尺度场的场强。这些强烈的小尺度磁特征可通过局部地壳屈服引发高能爆发，欧姆加热的局部增强可为恒星的持续辐射提供能量。因此，磁星行为中观测到的多样性可用能量相当的混合极向 - 环向场来解释。
