KMS of Xinjiang Astronomical Observatory, CAS
| 脉冲星射电辐射变化及辐射区特性的研究 | |
| Alternative Title | Investigations of the changes in pulsar radio radiation and the related properties of the emission regions |
涂作莹
| |
| Subtype | 博士 |
| Thesis Advisor | 王娜 |
| 2022-05-25 | |
| 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，单脉冲，辐射机制 |
| Abstract | 射电脉冲星的辐射展示出丰富多彩的辐射现象，其中包括模式变换、子脉冲漂移以及平均轮廓随频率的演化。通过对脉冲辐射现象的研究，可以探究脉冲星的辐射特性。本文通过研究PSR B0329+54的低辐射模式、脉冲星脉冲轮廓不同成分中的漂移子脉冲以及PSR B0355+54平均轮廓的多频演化，来探究相应的辐射特性。 PSR B0329+54是具有多成分、高强度且模式变换频繁发生的一颗脉冲星。我们使用新疆天文台南山25 m射电望远镜在中心频率为1.54 GHz对这颗源进行了约为15小时的单脉冲观测。通过研究发现，这颗脉冲星除了具有正常模式和反常模式辐射外，还具有低辐射模式（简称低模式）。在低模式下，这颗脉冲星平均轮廓的中心成分的辐射强度大幅下降且低于其他两成分的强度。该模式占总观测的3.6%,平均持续时间为3个脉冲周期。它在正常模式和反常模式下均可发生、且更频繁地发生在正常模式中。与正常模式和反常模式的累积轮廓相比，低模式的累积轮廓是独特的，其辐射特性与前面两种模式有关。通过对单脉冲的各个成分和整个脉冲的能量分析发现，引起中心成分辐射强度大幅下降的原因与其他两个成分无关。在正常模式中低模式辐射之后，脉冲星的辐射类似反常模式辐射，并在３个脉冲周期后逐渐恢复到正常模式。此外，在不同正常模式下低模式发生率基本上是一致的，这意味着低模式的持续时间与正常模式有关。研究结果表明，在特定的几何构型中，脉冲星的轮廓模式对应特定的磁层等离子体密度，模式变换意味着在轮廓的不同部分等离子体密度发生明显变化。 基于多辐射态的倾斜旋转脉冲星磁层模型，本论文研究了脉冲星不同脉冲轮廓成分中不同漂移子脉冲的辐射特性。假设子脉冲的辐射来自m离散区，这个离散区位于绕磁轴的“旋转木马”上。辐射状态的变化对应于漂移速率的变化。我们把这个模型应用于11颗脉冲星，它们在观测频率为1.4 GHz的脉冲轮廓不同部分呈现两个漂移带漂移的子脉冲。通过模拟确定不同漂移子脉冲的辐射状态以及辐射区域中的m相关值。结果表明，不同轮廓成分中的漂移子脉冲对应特定的辐射状态以及m值，并且不同的辐射状态和m可以共存于一个辐射区。我们确定了绕磁层的等离子体的循环时间，而且它与磁倾角相关。与另外3个具有单个漂移带的脉冲星相比，我们发现，当各自考虑不同的漂移带时，漂移子脉冲显示出相似的特性。基于我们的模型，同一轮廓中的不同漂移子脉冲的共存需要额外的机制，并且这种现象在具有较小磁倾角的脉冲星中比较常见。 脉冲星的平均轮廓通常随着频率的变化而变化。我们研究了PSR B0355+54的平均轮廓的多频演化。一部分数据来自于EPN数据库，另一部分是用南山25 m 以及昆明40 m的射电望远镜观测的数据。我们发现PSR B0355+54在1.54和2.256 GHz的频率下具有模式变换现象。当PSR B0355+54在1.54 GHz频率下的发生模式变换时，脉冲轮廓形状和轮廓宽度都发生了变换。当PSR B0355+54在频率为2.256 GHz下发生模式变换时，脉冲轮廓成分的相对峰值强度发生变化。我们发现PSR B0355+54的平均轮廓随频率的变化而变化。PSR B0355+54的脉冲轮廓宽度(W10)随频率(ν)的增加，并非遵循简单的递增或递减的趋势。我们发现PSR B0355+54的脉冲宽度W10在频率ν约为1 GHz时，存在反转，当ν<1 GHz时，脉冲宽度W10随频率ν的增加而增大；当ν ＞ 1 GHz时，脉冲宽度W10随频率ν的增加而减小。我们对W10和ν进行了拟合，粗略的发现它们符合对数－正态关系。目前我们仍然不清楚PSR B0355+54的平均轮廓的多频演化的辐射机制,需要进一步研究。 |
| Other Abstract | Emission from radio pulsars exhibits a variety of different phenomena. They include mode changing, sub-pulse drifting and the evolution of average profile with frequency. Through the investigation of the emission phenomena, we can explore the properties of radio emission from pulsars. In the thesis, we present the studies of the emission properties as revealed by the low emission mode in PSR B0329+54, properties of pulsar sub-pulse drifting in different profile components and the evolution of average pulse profile with frequency in PSR B0355+54. PSR B0329+54 is a radio pulsar with multi-component profile, high pulse intensity and frequent mode changing. We conduct single-pulse observations with total duration of 15 hours at the centre frequency of 1.54 GHz using the Nanshan 25 m radio telescope of Xinjiang Astronomical Observatory. Through the study of single pulses, we demonstrate that PSR B0329+54 exhibits another mode of emission, to which we name it the low emission mode (or low-mode), in addition to the normal and abnormal profile emission modes. In the low-mode, the intensities of the centre component of the average profile drops significantly below that of the other two components. The low-mode has an average duration of three pulse periods and is observed in both abnormal and normal emission modes of the pulsar occupying 3.6% of the observed pulses. We demonstrate that the properties of the low-modes are related to the two profile emission modes. We find that the average profile of low-modes is unique to the two modes, and that low-modes occur more frequently when the pulsar is in the normal mode. Analysis of the energy distribution for the low-modes in the normal emission modes suggests that the cause for the intensity drop in the central component is separated from the emission of the other two components. We demonstrate that the pulse emission characteristics in the normal emission mode shortly after a low-mode bears some similarities with the abnormal mode, and gradually recovering to the original normal emission in about three pulsar periods. In addition, the occurrence rate for low-modes in different normal modes is mostly consistent, which implies that the duration of low-modes is related to a normal mode for this pulsar. Our results imply profile modes each corresponds to specific magnetospheric plama density in particular geometric configuration, and profile mode changing signifies distinct changes of both at different parts of the profile. Based on the model for obliquely rotating pulsar magnetospheres of multiple emission states, we investigate the emission properties of the pulsars that exhibit different drifting subpulses in different pulse profile components. Emission from subpulses is assumed coming from m discrete areas located on carousels around the magnetic axis. An emission state is defined by this drift, and a change in the emission state corresponds to a change in the drift velocity. The model is applied to eight pulsars, all displaying drifting subpulses of particular properties along two different drift-bands at different parts of the pulse profile at frequency of 1.4 GHz. Simulation is performed to identify the emission states for the different drifting subpulses and the associated values of m in the emission region. The results show that drifting subpulses in different profile components correspond to particular emission states and m, and that different emission states and m can coexist in an emission region. We determine the circulation time for plasma around the magnetosphere and show that it is related to the obliquity angle. By comparing with three other pulsars that display drifting subpulses of single drift-band, we find that drifting subpulses demonstrate similar properties when consider the different drift-bands separately. We speculate, based on our results, that the coexistence of different drifting subpulses within a pulse profile may require additional mechanism, and the phenomenon is more common in pulsars with small obliquity angle. We study the evolution of the average profile in frequency as revealed by the pulsar PSR B0355+54. The data was obtained from the EPN database as well as from our observations using the Nanshan 25 m radio telescope of Xinjiang Astronomical Observatory and the Kunming 40 m radio telescope of Yunnan Astronomical Observatory. We find that PSR B0355+54 exhibits profile mode-changing at frequencies of 1.54 and 2.256 GHz. At 1.54 GHz, the shape and width of the average profile change when mode-changing occurs. However, the mode-changing at 2.256 GHz causes changes in the relative peak intensity between the profile components. In addition, the average profile changes in shape and profile width with frequency. Our results show that the change in profile width of the average profile does not follow a simple linearly increasing or decreasing trend as the frequency (ν) increases. When measuring the profile width at 10% of the intensity (W10), we find that the changes in the profile width demonstrate a turn-over that peaks at around 1 GHz. When ν < 1 GHz, W10 increases as the frequency increases, whereas W10 decreases with the increasing frequency for ν ＞ 1 GHz. We confirm that W10 and frequency ν follows a log-normal relation. The unique evolution of the average profile of PSR B0355+54 in frequency requires further investigation. |
| Pages | 98 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/5160 |
| 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 | 涂作莹. 脉冲星射电辐射变化及辐射区特性的研究[D]. 北京. 中国科学院大学,2022. |
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| 脉冲星射电辐射变化及辐射区特性的研究_涂（6172KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
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