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arXiv 2107.12911astro-ph.HE
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磁星的非轴对称进动与快速射电暴

Non-Axisymmetric Precession of Magnetars and Fast Radio Bursts

Ira Wasserman, James M. Cordes, Shami Chatterjee, Gauri Batra

摘要:

重复的FRB 180916.J0158和121102在连续发生的时间窗口期间可见。如果FRB~180916.J0158和FRB 121102观测到的周期性行为是由于磁星的进动,我们考虑了内部磁场和几何结构的约束。为了阻止涡旋线钉扎,我们认为内部磁场必须强于约$10^{16}$高斯,这是足够大,以防止超导的核心和破坏地壳晶格结构。我们推测进动磁星内部的磁场有三个分量:(1)具有特征强度$\sim 10^{14}$高斯的偶极分量;(2)具有特征强度$\sim 10^{15}-10^{16}$高斯的环形分量,它只占恒星体积的一小部分;(3)具有特征强度$\sim 10^{16}$高斯的无序场。无序场主要负责允许岁差,一旦这个场分量衰减,岁差就会停止,我们推测这会发生在$\sim 1000$年之后。可以想象,随着无序成分的衰减,爆发活动也会减弱并最终停止。我们模型的四极磁畸变的恒星,这是由于其有序的组件主要是三轴和很可能长。我们解决的问题,是否应该是可检测的旋进,爆裂磁星通过构建一个特定的模型,在该模型中,突发随机发生的时间与随机方向分布在锥或锥之间相对于一个单一的对称轴。在这些特定模型的背景下,我们发现,有进动的几何形状,检测自旋频率是非常不可能的。

英文摘要:

The repeating FRBs 180916.J0158 and 121102 are visible during periodically-occuring windows in time. We consider the constraints on internal magnetic fields and geometry if the cyclical behavior observed for FRB~180916.J0158 and FRB 121102 is due to precession of magnetars. In order to frustrate vortex line pinning we argue that internal magnetic fields must be stronger than about $10^{16}$ Gauss, which is large enough to prevent superconductivity in the core and destroy the crustal lattice structure. We conjecture that the magnetic field inside precessing magnetars has three components, (1) a dipole component with characteristic strength $\sim 10^{14}$ Gauss; (2) a toroidal component with characteristic strength $\sim 10^{15}-10^{16}$ Gauss which only occupies a modest fraction of the stellar volume; and (3) a disordered field with characteristic strength $\sim 10^{16}$ Gauss. The disordered field is primarily responsible for permitting precession, which stops once this field component decays away, which we conjecture happens after $\sim 1000$ years. Conceivably, as the disordered component damps bursting activity diminishes and eventually ceases. We model the quadrupolar magnetic distortion of the star, which is due to its ordered components primarily, as triaxial and very likely prolate. We address the question of whether or not the spin frequency ought to be detectable for precessing, bursting magnetars by constructing a specific model in which bursts happen randomly in time with random directions distributed in or between cones relative to a single symmetry axis. Within the context of these specific models, we find that there are precession geometries for which detecting the spin frequency is very unlikely.

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