脉冲星定时不规则性和磁场演化的印记
Pulsar timing irregularities and the imprint of magnetic field evolution
摘要：
孤立中子星的自转演化是由固定在恒星固体外壳上的磁场控制的。假设地核场在更长的时间尺度上演化，地壳场主要通过欧姆耗散和霍尔漂移演化，并且它可能会受到相对快速的变化，对观测到的时间特性产生显著影响。我们调查的磁场的结构和强度的变化，在恒星演化过程中可能有可观察到的后果，在制动指数，这是最敏感的量，以反映小的变化所造成的磁场重排的时间属性。通过对具有最先进微物理输入的中子星的磁热演化进行轴对称长期模拟，我们发现磁场演化对制动指数的影响可以根据年龄和内部温度分为三个定性不同的阶段：第一阶段可能与标准的电冰箱不同，（n~3）或低场中子星，在超新星爆炸过程中吸积回退物质（系统地n<3）;在第二阶段，演化由几乎纯欧姆场衰减控制，并且预期制动指数n>3;在第三阶段中，在后期，当内部温度已经下降到非常低的值时，中子星壳中的霍尔振荡模式导致制动指数的高绝对值和正负符号。具有强（1 e14 G）多极或环形分量的模型，甚至具有弱（~ 1 e12 G）偶极场的模型与观测到的时序特性趋势一致。
英文摘要：
(Abridged) The rotational evolution of isolated neutron stars is dominated by the magnetic field anchored to the solid crust of the star. Assuming that the core field evolves on much longer timescales, the crustal field evolves mainly though Ohmic dissipation and the Hall drift, and it may be subject to relatively rapid changes with remarkable effects on the observed timing properties. We investigate whether changes of the magnetic field structure and strength during the star evolution may have observable consequences in the braking index, which is the most sensitive quantity to reflect small variations of the timing properties that are caused by magnetic field rearrangements. By performing axisymmetric, long-term simulations of the magneto-thermal evolution of neutron stars with state-of-the-art microphysical inputs, we find that the effect of the magnetic field evolution on the braking index can be divided into three qualitatively different stages depending on the age and the internal temperature: a first stage that may be different for standard pulsars (with n~3) or low field neutron stars that accreted fallback matter during the supernova explosion (systematically n<3); in a second stage, the evolution is governed by almost pure Ohmic field decay, and a braking index n>3 is expected; in the third stage, at late times, when the interior temperature has dropped to very low values, Hall oscillatory modes in the neutron star crust result in braking indices of high absolute value and both positive and negative signs. Models with strong (1e14 G) multipolar or toroidal components, even with a weak (~1e12 G) dipolar field are consistent with the observed trend of the timing properties.
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