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arXiv 2109.07484astro-ph.HEastro-ph.SR
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磁星自旋演化的模拟

Modelling spin evolution of magnetars

Jedrzej A. Jawor, Thomas M. Tauris

摘要:

磁星(年轻的、极度磁化的中子星,NS)的起源和命运仍然没有解决。因此,探索它们的演化对于研究与其他孤立NS物种的可能联系至关重要,例如X射线暗NS(XDINS)和旋转无线电瞬变(RRAT)。在这里,我们研究磁星的自旋演化。两种途径的演变被认为是:一个指数衰减的B-字段,其他与子和超指数衰减。使用蒙特卡罗方法,我们合成磁星人口使用不同的输入分布和物理参数,如初始自旋周期,其时间导数和B-场衰减时标。此外,我们介绍了一个衰落的过程,可以占老磁星的衰落,我们简要地讨论了B-场和自旋轴的对齐的效果。我们将银河系核心坍缩超新星爆发率约为20 kyr^-1作为磁星诞生率的严格上限,并在输入参数研究中使用手动和自动优化算法将合成的粒子数与观测到的粒子数进行比较,我们发现B场必须以指数或超指数的方式衰减,其特征衰减时间尺度为0.5 ~ 10 kyr(最佳值为约4 kyr)。此外,初始旋转周期必须小于2秒。如果这些限制被保留,我们的结论是,有多种选择的输入物理,可以重现观测到的磁星人口相当不错。我们还得出结论,磁星很可能是进化联系到人口的XDINS,而他们一般不太可能演变成RRAT。

英文摘要:

The origin and fate of magnetars (young, extremely magnetized neutron stars, NSs) remain unsolved. Probing their evolution is therefore crucial for investigating possible links to other species of isolated NSs, such as the X-ray dim NSs (XDINSs) and rotating radio transients (RRATs). Here we investigate the spin evolution of magnetars. Two avenues of evolution are considered: one with exponentially decaying B-fields, the other with sub- and super-exponential decay. Using Monte Carlo methods, we synthesize magnetar populations using different input distributions and physical parameters, such as for the initial spin period, its time derivative and the B-field decay timescale. Additionally, we introduce a fade-away procedure that can account for the fading of old magnetars, and we briefly discuss the effect of alignment of the B-field and spin axes. Imposing the Galactic core-collapse supernova rate of ~20 kyr^-1 as a strict upper limit on the magnetar birthrate and comparing the synthetic populations to the observed one using both manual and automatic optimization algorithms for our input parameter study, we find that the B-field must decay exponentially or super-exponentially with a characteristic decay timescale of 0.5-10 kyr (with a best value of ~4 kyr). In addition, the initial spin period must be less than 2 sec. If these constraints are kept, we conclude that there are multiple choices of input physics that can reproduce the observed magnetar population reasonably well. We also conclude that magnetars may well be evolutionary linked to the population of XDINSs, whereas they are in general unlikely to evolve into RRATs.

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