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脉冲星的星⻛制动模型以及脉冲星周期跃变和磁层关系的研究
Alternative TitleThe Wind Braking Model and Connection between Pulsar Glitch Activity and Magnetospheric Behavior
寇菲菲
Subtype博士
Thesis Advisor王娜 ; 仝号
2018-06
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Name理学博士
Degree Discipline天体物理
Keyword中子星 脉冲星 周期跃变 模式变换 星风制动模型
Abstract通过对制动指数的观测可以探究脉冲星自转减慢的制动机制,目前有11颗年轻脉冲星有长期稳定的制动指数,但是大部分脉冲星的并不稳定,甚至被计时噪声所左右。此外观测发现年轻脉冲星的自转更加不稳定,表现为自转减慢率或制动指数的变化。如何自治的理解这些观测现象成为研究脉冲星制动机制的挑战。但是间歇脉冲星的发现为研究脉冲星辐射和自转提供了新思路,其他几颗脉冲星的观测发现,脉冲轮廓随自转减慢率的变化而不同,这些观测现象说明脉冲星的自转和辐射是相关联的。 星风制动模型是在考虑磁层中粒子加速和辐射过程下建立起来的,因此可以将脉冲星的辐射和自转减慢自然地联系起来。我们通过考虑磁层加速区中的粒子效应,磁倾角和自转的联合演化以及辐射停止后的“死亡”效应来完善星风制动模型。在星风制动模型下,随着脉冲星自转减慢,脉冲星会由磁偶极辐射制动主导演化到由粒子辐射制动主导,预期的制动指数介于1和3之间,因此可以自然地解释年轻脉冲星小于3的制动指数的观测;而考虑磁倾角和自转的联合演化后,脉冲星的磁倾角在制动力矩驱使下会逐渐减小(自转轴和磁轴趋于平行),因此脉冲星的制动指数在磁偶极辐射制动主导阶段会大于3,可以解释PSRJ1640-4631的制动指数的观测。利用Crab脉冲星相对较全面的观测信息,计算发现磁层加速区中的初级粒子密度至少为100倍的GJ电荷密度。磁层性质与磁层中的粒子息息相关,因此粒子密度的变化将会导致脉冲星的自转不稳定性,实际上粒子密度的变化有两种形式,将分别导致不同的观测现象:磁层加速区中初级粒子密度幅度比较大的增大或减小,会影响脉冲星的制动力矩,从而导致脉冲星自转频率的变化;磁层加速区中初级粒子密度随时间实时的变化,会影响制动力矩的变化率,从而导致脉冲星自转频率更高阶的变化,比如,也就是制动指数(n)。此外,粒子密度的随机起伏将会导致的随机变化。考虑脉冲星的“死亡”效应后,正常脉冲星(包括年轻脉冲星)在周期-周期导数图上最终会向“死亡谷”演化,因此磁星并不是由年轻脉冲星演化而来。 在大多数周期跃变发生时,并没有观测到辐射特征的变化。然而最近的观测发现年轻脉冲星的自转减慢率或制动指数在跃变后发生变化(扣除跃变参数后)。更有趣的是,三颗射电脉冲星在跃变时,自转减慢状态和辐射模式发生变化,这为探究脉冲星内部结构和边部磁层的关系提供了观测依据。 我们利用南山观测站对脉冲星的到达时间观测数据,分析PSRB2035+36的长期自转减慢行为和脉冲轮廓变化,发现PSRB2035+36在MJD52950发生一次幅度比较小的跃变,△v/v~7.7(8)×10^(-9),但是跃变时自转频率的相对变化比较大,A/v~0.067(8);跃变后的800天内自转减慢率持续增大,与正常跃变后自转减慢率的变化趋势相反,且跃变后自转减慢率比跃变前平均增大了9.6%;跃变前自转减慢率有明显起伏,但是跃变后很稳定。此外,辐射模式也伴随跃变发生明显变化:跃变后脉冲轮廓变窄;跃变后有两种稳定积分脉冲轮廓(辐射模式),脉冲星在这两种辐射模式间切换;长期来看窄的脉冲轮廓主导趋势越来越明显。 脉冲星的周期跃变一般认为是星体内部结构变化导致的;自转减慢率变化和辐射变化一般认为来自于星体外部磁层的起伏。PSRB2035+36的观测说明磁层的变化与周期跃变有关,也就是说星体内部结构的变化有可能导致外部磁层的起伏。
Other AbstractObservationally,11 young pulsars show stable second derivatives of the spin frequency(), and give the braking index measurements. However, the second derivatives of most pulsars are not stable and have abnormal distribution. Besides, variable spindown behaviors such as variations in the spin-down rate and the braking index are alsofound in a few young pulsars. All of these observations make contradiction with classi-cal understanding. Studies of the intermittent pulsar lead to a significant advancement in the understanding of pulsar timing and radiation.A more unusual aspect of the pulsar rotation is that the timing behaviors of a few pulsars coincide with changes of their pulse profiles. These observations indicate that there are correlation between pulsar spin-down and emission. A wind braking model was proposed based on the process of particle acceleration and radiation in a physical magnetosphere, which naturally linked the pulsar spin-down and emission. We update the wind braking model by considering the effect of particle density, the combined evolution of inclination angle and spin-down rate, and the efect of pulsar death. It can describe both the short-term and long-term rotational evolution of pulsars consistently. In the wind braking model, as the pulsar spins down, the pulsar will evolve form the magnetic dipole radiation dominated case towards particle winddominated case, the braking index will decrease from about 3 to about 1. However, by considering the combined evolution of inclination angle and spin-down rate in a3-D magnetosphere, the braking index wil be larger than 3 in the magnetic dipole radiation dominated case. Hence, the wind braking model could explain the existence of a high braking index larger than three and a low braking index simultaneously. The primary particle density in acceleration region is at least 100 times the Goldreich-Julian charge density. The particle density reflects the magnetospheric activity in real-time and may be responsible for the changing spin-down behavior.A larger particle density will re-sult in an increase in the spin down rate and predicts a smaller braking index, and an increasing particle density will lead to a lower braking index. Besides, The fluctuation in the neutron star magnetosphere can be either periodic or random, which result in anomalous frequency second derivative and they have similar results. Considering the efect of pulsar "death", the young pulsars(and other normal pulsars) will not evolve to the cluster of magnetars but downwards to the death valley. For most glitch events, there are no radiative and pulse profile changes observed. However, variable braking indices and spin-down rates between glitches are observed after removal of the effects of the glitches. What's more interksting is the that significant changes in the spin down state and pulse profile accompanied with glitch activity are observed for a few pulsar. All of these observations indicate that there should be connection between magnetospheric behavior and glitch events. We presente timing results of PSR B2035+36 using~9-yr observations with the Nanshan 25-m radio telescope. PSR B2035+36 was reported to exhibit significant changes in pulse profile correlated with spin-down state variations. We find that the pulsar underwent a glitch with a jump in the frequency of Av~12.4(5) nHz around MJD 52950. Unusually, the spin-down rate increased persistently over 800 days after the glitch, and the average spin-down rate of post-glitch was about 9.6% larger than pre-glitch. Accompanied with the glitch activity, pulse profile became narrower. The pulsar began to switch between two emission modes after the glitch, with pulse width(W somean) of 8.5(7) and 3.7(3), respectively. Besides that, the relatively narrow pulse profile gradually became dominant. All of the observations indicate that there should be connection between magnetospheric behavior and glitch activity. We discuss one possibility of magnetospheric fluctuation triggered by glitch event.
Pages100
Language中文
Document Type学位论文
Identifierhttp://ir.xao.ac.cn/handle/45760611-7/2482
Collection研究生学位论文
Affiliation中国科学院新疆天文台
First Author AffilicationXinjiang Astronomical Observatory, Chinese Academy of Sciences
Recommended Citation
GB/T 7714
寇菲菲. 脉冲星的星⻛制动模型以及脉冲星周期跃变和磁层关系的研究[D]. 北京. 中国科学院大学,2018.
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