Magnetars are comparatively young neutron stars with ultra-strong surface magnetic field in the range 1014–1016G. The old neutron stars have surface magnetic field somewhat less ∼108G which clearly indicates the decay of field with time. One possible way of magnetic field decay is by ambipolar diffusion. We describe the general procedure to solve for the ambipolar velocity inside the star core without any approximation. With a realistic model of neutron star, we determine the ambipolar velocity configuration inside the neutron star core and hence find the ambipolar decay rate, associated timescales and the magnetic energy dissipated which is consistent with the magnetar observations.

中文翻译：

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磁星中磁场的双极衰减和观察到的磁星活动

磁星是相对年轻的中子星，在该范围内具有超强的表面磁场1014–1016G. 老中子星的表面磁场稍弱 ～108G这清楚地表明了场随时间的衰减。一种可能的磁场衰减方式是通过双极扩散。我们描述了在没有任何近似的情况下求解星核内双极速度的一般程序。通过中子星的真实模型，我们确定了中子星核心内部的双极速度配置，从而找到了与磁星观测一致的双极衰变率、相关时间尺度和耗散的磁能。