KMS of Xinjiang Astronomical Observatory, CAS
| 双磁偶极子模型和磁星制动指数的研究 | |
| Alternative Title | A study of double magnetic-dipole model and magnetar braking index |
闫方洲
| |
| Subtype | 硕士 |
| Thesis Advisor | 高志福 |
| 2021-06-01 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Name | 理学硕士 |
| Degree Discipline | 天体物理 |
| Keyword | 双磁偶极子模型 磁星的制动指数 SGR0501+4516 1E2259+586 |
| Abstract | 磁星是靠磁场能提供能量的一类脉冲星。对磁星的观测与理论研究是当前脉冲星领域一个重要的热点。磁星大致分为软伽马射线重复暴和反常X射线脉冲星磁星表现出一系列的X-射线活动性，如短暴、长暴、耀斑和准周期震荡，通常伴随着一系列到达时间行为，如周期跃变和反周期跃变等，这些活动性被认为是内部超强磁场衰减引起的，同时影响到磁星的自转演化。制动指数是一个可被观测的物理量(用n 来表示)。对制动指数的研究不仅可以揭示脉冲星的辐射特性和内部物理，而且有利于预测脉冲星的自转演化。在第一章，我们简单地介绍脉冲星基本知识、磁星及本文的研究内容和意义；第二章介绍了关于中子星内部磁场起源的双磁偶极子模型，并应用该模型，按照双磁偶极子模型，中子星内部有两个磁矩，磁矩M1由带电体旋转产生，磁矩M2是顺磁材料磁化产生。我们的计算表明：在三个高值制动指数 (n > 3)磁星 SGR 0501+4516、1E2259+586 和1E 1841-045的内部，磁矩M2将朝着旋转轴的方向转动造成磁倾角的减小，这就自然地解释了磁星高值制动指数。PSR J1640-4631是目前观测上发现的第一颗制动指数超出磁偶极辐射模型预言n = 3。我们定义一个反映中子星磁化程度比值：η = M2/M，假设三颗高制动指数磁星拥有相同的磁倾角变化率，得到了磁星的η值要大于依靠旋转供能脉冲星PSR J1640-4631的η值;在第三章，我们首先介绍了脉冲星制动指数最新研究进展，然后在真空模型下推导出新的制动指数表达式，并计算了几个年轻脉冲星的制动指数，得到的结果比较可靠。相比于传统的脉冲星制动指数的定义式，本文所得的制动指数表达式不必依赖于自转周期二阶导数，非常方便和适用；第四章对全文进行总结，并对未来进行展望。本文的研究结果将为（包括磁星在内的）年轻脉冲星的自转演化和辐射机制的研究提供了一个新窗口，本文给出的理论模型会在未来的观测中得到检验和发展。 |
| Other Abstract | Magnetar are a kind of pulsars whose energy is provided by superhigh magnetic fields. The study on magnetars is an important hotspot in the field of pulsars. Magnetars can be roughly divided into soft gamma-ray repeat bursts and anomalous X-ray pulsars. Magnetars exhibit a series of X-ray activities, such as short bursts, long bursts, flares and quasi periodic oscillations. These activities are usually accompanied by a series of timing behaviors, such as glitches and anti-glitches, which are considered to be caused by the decay of the internal magnetic fields, affecting the rotation evolution of magnetars. The braking index is an observable physical quantity (denoted as n). The study of the braking index can not only reveal the radiation characteristics and internal physics of pulsars, but also is helpful to predict the rotation evolution of stars. The first chapter as the preface briefs the basic knowledge of pulsars, magnetars and the research content and significance. In the second chapter, we introduce the double magnetic-dipole model on the origin of internal magnetic fields of neutron stars and apply it to explain high braking indices of magnetars. In this model, there are two magnetic moments inside a neutron star—one is generated by the rotation effect of a charged sphere, M1, and the other is generated by the magnetization of ferromagnetically ordered material, M2. Our calculations indicate that the magnetic moment M2 would evolve toward alignment with the spin axis for the three magnetars SGR 0501 + 4516, 1E 2259 + 586 and 1E 1841-045 and cause their magnetic inclination angles to decrease. which naturally explains the high braking indices of magnetars. We also define a ratio ��� = M2/M1, which reflects the magnetization degree, and find that the values of ��� of three magnetars are about two orders of magnitude higher than that of rotationally powered pulsar PSR J1640-4631 with n = 3.15(3), assuming that they have the same rate of decrease in their inclination angles. In the third chapter, we first introduce the latest research progress of pulsar braking index, then calculate the values of n for several young pulsars by derive a new expression of the braking index under the vacuum model, and the calculation results are reliable. The expression of braking index obtained in this paper does not depend on the second derivative of rotation period. Compared with the traditional definition of pulsar’s braking index, the new expression of n in this thesis is very convenient and applicable. The fourth chapter summaries the full text, and makes a prospect and an approach to further development. The results of this thesis will provide a new window for the study of the rotation evolution and radiation mechanism of young pulsars (including magnetars). Our theoretical model will be tested and developed in future observations. |
| Pages | 46 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/4738 |
| Collection | 研究生学位论文 |
| Affiliation | 中国科学院新疆天文台 |
| First Author Affilication | Xinjiang Astronomical Observatory, Chinese Academy of Sciences |
| Recommended Citation GB/T 7714 | 闫方洲. 双磁偶极子模型和磁星制动指数的研究[D]. 北京. 中国科学院大学,2021. |
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