KMS of Xinjiang Astronomical Observatory, CAS
| 射电脉冲星单脉冲特性的观测研究 | |
| Alternative Title | Individual pulse emission properties of radio pulsars |
温志刚
| |
| Subtype | 博士 |
| Thesis Advisor | 王娜 |
| 2016 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 天体物理 |
| Keyword | 脉冲星 单脉冲 快速射电暴 |
| Abstract | 本文研究内容涉及作者在研究生阶段的科研工作。这些工作主要集中在脉冲星单脉冲辐射特性方面的研究上。脉冲星单个脉冲反映了脉冲星具体的辐射过程，相关研究对深入理解脉冲星辐射的机制和具体物理过程有重要意义。 本文第一章概述了射电脉冲星的基本性质，包括脉冲星的观测特征和导出的参数，脉冲星的几何模型和辐射机制等。 本文第二章研究了PSR B2020+28的模式变换特性。通过南山25米射电望远镜在频率为1556 MHz的连续观测，发现它的前导和后随成分的相对强度比的统计呈现出具有拖尾的高斯分布，这说明这颗脉冲星存在两种辐射模式。在我们的数据中共探测到了76次模式变换事件，正常模式和反常模式出现的概率分别为89%和11%。反常模式的分布比正常模式更窄，这表明反常模式比正常模式更加稳定。我们对正反常模式的內秉持续时标进行了限定，二者都可以通过幂率分布很好的描述，但是谱指数差别较大，这可能表明反常模式变得稳定所需的时间比正常模式更短。正反常模式之间的频繁转换也表明脉冲星磁层态之间的快速震荡。我们首次成功地限定PSR B2020+28的内秉持续时标，这为我们从物理上理解脉冲星模式变换特性提供了非常宝贵的信息。 本文第三章展示了我们对PSR J1727?2739的脉冲缺失和子脉冲漂移特性的研究。通过Parkes在中心频率为1518 MHz的单脉冲观测，我们共探测到5568个单脉冲。探测到的零脉冲的持续时标从6 到281个脉冲周期。脉冲缺失比大约为68%。爆发态的持续时标从2到133个周期，在脉冲缺失态也偶尔探测到了强脉冲信号。将所有的零脉冲进行折叠后得到的平均轮廓没有探测到信噪比大于3的信号。从脉冲缺失态到爆发态的转变非常迅速，而从爆发态转变为脉冲缺失态则表现出快速和慢速两种形态。而且我们探测到了两种子脉冲漂移模式，我们称之为模式A和B，他们分别对应的漂移带的周期为9.7±1.6和5.2±0.9个脉冲周期。这颗脉冲星有时也会出现无漂移状态，我们称之为模式C。有些模式之间的转变非常快速，但是也有些在经过脉冲缺失态以后才会切换。不同的漂移模式具有不同的平均脉冲轮廓。这些辐射特性对我们理解脉冲星的辐射机制具有极大的意义。 本文第四章展示的是对PSR B1237+25的单脉冲辐射特性的研究。利用南山25米射电望远镜，我们在1540 MHz连续观测了大约7小时，共探测到了793个信噪比大于5的强脉冲信号。通过对这些强脉冲的到达时间进行分析，发现残差图呈现一个五带的分布，这与平均轮廓的五个辐射成分相吻合，表明强脉冲与平均脉冲相同，都是来自于磁层内的五个辐射区。位于中心成分处的强脉冲辐射最为复杂，探测到了最强和最宽的爆发。这些强脉冲的信噪比、峰值流量密度比和脉冲宽度符合幂率分布，对应的谱指数分别为：5.12、2.98和3.52。强脉冲比平均脉冲轮廓窄大约11倍，峰值流量密度是平均脉冲轮廓的10.2到80.2倍。按照强脉冲的结构可以分为五种单峰的爆发和3种双峰爆发。PSR B1237+25和PSRs B0031?07，B1112+50，J1752+2359，B0656+14，B0950+08的强脉冲的辐射机制可能是相同的，它们在光速圆柱处的磁磁场都比较弱，并且峰值流量密度的谱指数都大于2。而且我们首次在1540 MHz探测到了位于核成分周围的两个新的辐射成分，之后我们通过延迟和偏差效应对三个辐射锥的结构进行了详细的分析。 本文第五章研究了PSR B1133+16在322 MHz的强脉冲辐射特性。我们利用印度巨型米波射电望远对其进行了长达8小时的连续单脉冲观测，共探测到了1082个强脉冲信号，它们的峰值能量与平均脉冲轮廓的比值在10到23之间。大部分强脉冲都分布在平均脉冲轮廓的前导和后随成分处，前导成分探测到的强脉冲是后随成分的2.74倍。所有单脉冲的能量可以用两个高斯成分和一个截断的幂率分布进行很好的拟合，其中谱指数为α= ?3.8。 然后我们对相位在前导成分的793个强脉冲进行了相位分离的涨落谱分析，在前导成分处发现了一个极低频的相位调制，对应的频率为f ? 0.0116 c/P1。 本文第六章首先展示了我们利用云南40米射电望远镜对三次伽马暴进行跟踪观测，观测频率为2256 MHz。我们对得到的单脉冲数据在色散量为0到5000 pc/cm3内进行消色散，步长为50 pc/cm3。 在伽马暴后的时间内没有探测到信噪比大于5的类似于快速射电暴的信号。如果快速射电暴与伽马暴成协的话，那么依据望远镜的灵敏度我们可以得到GRB140512A、GRB140629A 和140703A 的流量密度上限分别为2.5，8.0和8.0 Jy。通过对数据进行统计分析表明探测到信噪比大于5的信号来自于热噪声的涨落。最后我们讨论了利用南山26米射电望远镜进行与伽马暴成协的快速射电暴搜寻的可能性。随着观测设备的灵敏度的不断提高和搜寻算法的不断优化，在不久的将来会有大批的与伽马暴成协的快速射电暴被探测到。其次我们利用欧洲甚长基线干涉网（EVN）的相位参考观测模式对RRAT J1819?1458 在L波段进行了观测。首次通过干涉技术对单脉冲信号进行成像，测得了目前最精确的位置。由于旋转射电暂现源具有与快速射电暴相似的辐射特性，因此这个研究证明利用欧洲甚长基线干涉网进行快速射电暴的搜寻和定位是可行的。 |
| Other Abstract | This thesis mainly introduces the project accomplished during my graduate study period. These studies focused on the individual pulse emission properties of radio pulsars. In the first chapter, we review the main emission properties of pulsars, empirical models and emission mechanism.The second chapter reports on polarimetric radiation properties based on the switching modes of normal PSR B2020+28 by analysing the data acquired from the Nanshan 25-m radio telescope at 1556 MHz. With nearly 8 hours quasi-continuous observation, the data presented some striking and updated phenomena. The change of relative intensity between the leading and trailing components is the predominant feature of mode switching. The intensity ratio between the leading and trailing components are measured for the individual profiles averaged over 30 seconds. It is found that there is an excess of high ratios over the normal distribution, which indicates that two modes exist in the pulsar. The distribution of abnormal mode has a narrower width indicating that the abnormal mode is more stable than the normal mode. A total of 76 mode switching events are detected in our data. It spends 89% in the normal mode and 11% in the abnormal mode. The intrinsic distributions of mode timescales are constrained with power-law distributions. The significant difference in the index of the duration distribution between normal and abnormal modes possibly indicates that the timescale for the abnormal mode to get stable is shorter than that for the normal mode. The frequent switching between both modes may indicate that the oscillations between different magnetospheric states are rapid.In chapter 3, we make a detailed study of the nulling and subpulse drifting in PSR J1727?2739 for investigation of its radiation properties. The observations were carried out on 20 March, 2004 using the Parkes 64-m radio telescope, with a central frequency of 1518 MHz. A total of 5568 single pulses were analysed. This pulsar shows well defined nulls with lengths lasting from 6 to 281 pulses and separated by burst phases ranging from 2 to 133 pulses. We estimate a nulling fraction of around 68%. No emission in the average pulse profile integrated over all null pulses is detected with significance above 3σ. Most transitions from nulls to bursts are within a few pulses, whereas the transitions from bursts to nulls exhibit two patterns of decay: decrease gradually or rapidly. In the burst phase, we find that there are two distinct subpulse drift modes with vertical spacing between the drift bands of 9.7±1.6 and 5.2±0.9 pulse periods, while sometimes there is a third mode with no subpulse drifting. Some mode transitions occur within a single burst, while others are separated by nulls. Different modes have different average pulse profiles. Possible physical mechanisms are discussed.Chapter 4 presents results on individual pulse studies of PSR B1237+25. A total of 793 strong pulses with signal-to-noise ratios above 5 threshold were detected at 1540 MHz in nearly 7-hour observational data. A five-band distribution of timing residuals is confirmed and the strong pulses are all distributed within the five emission components of the pulse profile. This leads us to believe that there is no difference in the basic emission mechanism of the five components, and confirms that the strong pulses are emitted from the same region of the magnetosphere as the average pulses. The strong pulses in the central component, including the brightest and widest bursts, are extremely complicated. The strong pulses are narrower than average pulse profiles by a factor of nearly 11. The peak flux densities are from 10.2 to 80.2 times that of average pulse profile. The structures of strong pulses can be divided into five types of unimodal burst and three types of bimodal burst. The statistical properties of signal-to-noise ratios, W50and peak flux densities of these bursts are described by their power-law indices, which are 5.12, 2.98 and 3.52 respectively. PSR B1237+25 as well as the previously detected in PSR B0031?07, PSR B1112+50, PSR J1752+2359, PSR B0656+14 and PSR B0950+08, belong to the group of pulsars which emit strong pulses without strong magnetic fields at the light cylinder and whose power-law indices of peak flux densities are all larger than 2. Furthermore, a weak inner- most conne around the core is firstly discovered at our observing frequency, and the detailed analysis of the structures of three connes are carried out.Chapter 5 presents a detailed study on the strong pulse emission from PSR B1133+16. The high time resolution data (61 μs) were obtained with the Giant Metrewave Radio Telescope at a central frequency of 322 MHz across a bandwidth of 32 MHz. In a continuous observation of 7.45 hours, a total of 1082 strong pulses with peak flux density ranging from 10 to 23 times of that of the average pulse are detected sporadically. Most of them are located in the leading and trailing windows of the average pulse profile, and the ratio of the numbers is about 2.74. The distribution of pulse energy of all individual pulses can be described by a combination of two Gaussian components and a cut-off power-law with index of α = ?3.8. The longitude-resolved fluctuation spectral analysis is performed on the sequence of 793 separated strong pulses in the leading longitudes. It is imperative that an extremely low-frequency feature associated with phase modulation at f ? 0.0116 c/P1is identified in the leading component for the first time.In the first section of chapter 6, we report on the results of three GRBs notificated by the Burst Alert Telescope on board the Swift satellite at 2256 MHz using a 40-m radio telescope located at the YunNan Astronomical Observatory. Single radio pulses are searched in a large range of dispersion measure from 0 to 5000 pc/cm3 with steps of 50 pc/cm3. No FRB-like emission from the prompt phase of GRBs are detected with significance larger than 5σ. If there are FRBs related to the GRBs, we set an upper limit on the flux density of radio pulses of 2.5 Jy for GRB140512A and 8.0 Jy for GRBs 140629A and 140703A with the sensitivity of the telescope. A statistical analysis of the GRB data reveals that the events detected above 5σ are consistent with the thermal noise fluctuations. A short prospects are described to observe FRBs associated with GRBs with NanShan refined 26-m radio telescope at 1540 MHz systematically. A significant number of searches for FRBs associated with GRBs will be expanded in the near future. Then we present the first successful e-EVN phase-referencing observations of the RRAT J1819?1458 on May 13, 2015 at L band. The most accurate position was determined by imaging the single pulses. |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/1724 |
| Collection | 研究生学位论文 射电天文研究室 |
| Affiliation | 中国科学院新疆天文台 |
| Recommended Citation GB/T 7714 | 温志刚. 射电脉冲星单脉冲特性的观测研究[D]. 北京. 中国科学院大学,2016. |
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