KMS of Xinjiang Astronomical Observatory, CAS
| 脉冲星中爆发现象的研究 | |
| Alternative Title | The study of burst phenomena in pulsars |
孙盛楠
| |
| Subtype | 博士 |
| Thesis Advisor | 王娜 |
| 2021-12-01 | |
| 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,巨脉冲,周期性 |
| Abstract | 脉冲星的辐射通常表现出多种多样的变化，有些脉冲星会突然产生非常亮 的单脉冲辐射，其能量比平均脉冲能量高出 10 倍甚至更多，这种现象称之为巨 脉冲，持续时间最短为几个纳秒。到目前为止仅在 16 颗脉冲星中发现了巨脉冲， 包括 11 颗正常脉冲星和 5 颗毫秒脉冲星。巨脉冲的能量服从幂律分布，而正常的 脉冲服从高斯或对数正态分布，这两种不同的脉冲能量分布表明它们的辐射机 制不同。在第一个工作中，我们使用 Parkes 64-m 望远镜观测研究 PSR J1047-6709 的辐射变化。我们发现这颗脉冲星表现出两种不同的辐射状态: 弱辐射态和亮辐 射态，并且首次在亮态下探测到了巨脉冲。这是我们发现的新的巨脉冲脉冲星。 我们共发现有 75 个巨脉冲，其脉冲宽度在 0.6 到 2.6 ms，能量呈现幂律分布，指 数为：𝛼 = −3.26 ± 0.22。最亮的巨脉冲的峰值流量密度为 19 Jy，是平均脉冲轮 廓峰值流量密度的 110 倍。我们进一步分析发现巨脉冲的平均脉冲轮廓的偏振 特性与亮态下其它脉冲的平均脉冲轮廓的偏振特性相似，该发现表明这两类脉 冲有相同的辐射起源，表现形式仅为能量的差别。我们的研究结果为脉冲星的巨 脉冲起源提供了新的视角。 有些脉冲星会产生突然的爆发，但其能量弱于巨脉冲，这种脉冲星称为爆脉 冲星。在我们的另一个工作中，我们用 500 米口径球面射电望远镜（FAST）在 观测了三颗爆脉冲星:PSR J1752+2359，PSR J0614+2229 和 PSR J1938+2213。我 们发现 PSR J1752+2359 显示了两种不同的辐射状态: 连续的正常脉冲辐射状态 和类似于旋转射电暂现源一样的零星辐射状态。PSR J1752+2359 是所发现的第 三颗在旋转射电暂现源和正常脉冲星之间转换的脉冲星。这颗脉冲星只有 20% 的时间处于正常态，在两个态之间的转换是周期性的，其转换周期约为 568 个 脉冲周期。这两种辐射态的平均脉冲的偏振轮廓不同，而且偏振角也呈现不同 的变化，其轮廓峰值之间有约为 0.35° 的偏移。我们的结果表明，这颗源在两种 状态下脉冲星的磁层的几何结构可能发生了改变。PSR J0614+2229 呈现 A 和 B 两种不同的辐射态，其中 A 态的辐射在相位上早于 B 态，这两种辐射态的平均 脉冲轮廓偏振特性不同。我们还发现在两种辐射态之间的转换过程中脉冲辐射 变亮，这可能与模式变换的某种触发机制相关，类似现象还没有在其它模式变换脉冲星中发现。PSR J1938+2213 是由一个较弱的辐射态和较亮的爆发态叠加而 成，其中弱辐射态一直存在，爆发态最高可达到平均脉冲能量的 57 倍。这两种 辐射态的偏振特性也不同。我们还在爆发态发现正交偏振模式，而弱态并没有呈现此现象，这表明这两种辐射态的等离子体环境不同。我们的结论表明，PSR J1938+2213 的两种辐射态可能产生在脉冲星磁层中的不同区域。 我们目前正在使用澳大利亚 Parkes 望远镜超宽带接收机（UWL）对周期性 振幅调制的脉冲星进行研究。UWL 从 704 MHz 到 4032 MHz 连续覆盖，为研究 脉冲星辐射在超宽频带的变化提供了难得的机会。我们通过对五颗周期性振幅 调制的脉冲星观测分析发现这类脉冲星虽然在强度上有明显的亮暗变化，但是 其能量仅为单峰分布。这类周期性振幅调制现象可能是一种特殊的模式变换。我 们把其中的能量高于平均脉冲能量的脉冲成为亮辐射态，反之则称为弱辐射态。 通过对不同辐射态进行偏振分析，我们发现 PSR J0624−0424，PSR J1430−6623， PSR J1653−3838 和 PSR J1722−3207 在亮和弱两种辐射态的偏振位置角相同；而 PSR J1534−5334 不同态的偏振位置角不同。偏振位置角的变化与脉冲星磁层结 构或者辐射区的位置相关。我们的研究表明这类振幅调制脉冲星在不同态的磁 层结构保持不变，其辐射变化可能是由于磁层中粒子流的变化导致，而辐射区域 的高度的改变将会导致偏振位置角的变化。 |
| Other Abstract | Pulsars typically show a variety of variations in their emission. Some pulsars suddenly show short-duration strong burst emission, whose energy is 10 times or more higher than that of the average pulse energy. This phenomenon is called giant pulses that typically last for a few nanoseconds. So far, this phenomenon has only been detected in 16 pulsars, including 11 normal pulsars and 5 millisecond pulsars. Generally, giant pulses are related to high energy emissions. The energy distribution of giant pulse obeys a power-law distribution, while that of normal pulse follows a normal or a log-normal distribution. In our first work, we report the emission variations in PSR J1047-6709 observed at 1369 MHz using the Parkes 64-m radio telescope. The pulsar shows two different emission states: a weak state, a bright emission state. For the first time, we detected giant pulses in the bright state. This is a new giant-pulse emitting. We found 75 giant pulses with pulse width between 0.6 and 2.6 ms. The energy of these giant pulses present a power-law distribution with the index of 𝛼 = -3.26 ± 0.22. The peak flux density of the brightest giant pulse is 19 Jy, which is 110 times of the peak flux density of the average pulse profile. In the bright state, the polarization properties of the average pulse profile of the giant pulse are similar to those of the average pulse profile with energy less than 10 times of the average pulse energy. The results show that in the bright state, the giant pulse and the pulse with energy less than 10 times of the average pulse energy have the same emission mechanism. Our results provide a new clue for the origin of giant pulses in pulsars. Some pulsars show sudden bursts weaker than giant pulses, which are called bursting pulsars. In our another work, we present the observations of three bursting pulsars PSRs J1752+2359, J0614+2229 and J1938+2213 at 1250 MHz using the Five hundred meter Aperture Spherical radio Telescope (FAST). We find that PSR J1752+2359 shows two states: a normal state with continuous pulse emissions and a rotating radio transient like state with sporadic emissions. This pulsar is present 20% of the time in the normal state. The state-switching of this pulsar is quasi-periodical with a period of about 568 pulse periods. The polarization profiles of the average profiles in the two states are different. Also, the PA swings for them are different. There is a slight pulse phase offset of the profile peaks between the two states, which is about 0.35°. Our results suggest that the pulsar magnetosphere geometries in the two states are different. PSR J0614+2229 shows two distinct emission states, in which the emission of state A occurs earlier than state B in longitude. The polarization properties of the average profile of the two states are different. We also found that the emission becomes much brighter during the transition between the two states, which may be related to the trigger mechanism of mode switching. Similar phenomena have never been seen in other mode-changing pulsars before. PSR J1938+2213 appears to consist of a weak emission state superposed by brighter burst emissions. The weak state is always present and the brightest pulse in burst state is about 57 times larger than the average pulse energy. The polarization properties of the two states are also different. The orthogonal polarization mode phenomenon is only seen in the burst state, rather than both states, indicating that the plasma environments of the two emission states are different. Our results suggested that the emission for the two states of PSR J0614+2229 and J1938+2213 may be generated in different regions of the pulsar magnetosphere. We are currently working on periodic amplitude modulation pulsars using the Australian Parkes Telescope Ultra-Wideband Receiver (UWL). UWL covers continuously from 704 MHz to 4032 MHz, which provides a rare opportunity to study the variation of pulsar emission in a wide frequency range. Our analysis of five pulsars with amplitude modulation shows that these pulsars have significant variations in intensity, but show unimodal energy distribution. Such amplitude modulation pulsars may be a special kind of periodic mode change pulsar. We define pulses with energy higher than that of the average pulse as bright state, and those with energy lower than that of the average pulse as weak state. By analyzing their polarization properties of two states, we found that the linear polarization position angles of different states are similar for PSRs J0624-0424, J1430-6623, J1653-3838 and J1722-3207, while for PSR J1534-5334, the linear position angles of different states are different. Our study shows that the magnetosphere geometries in different states remains unchanged, which attributed to the different distributions of magnetospheric currents. However, the change of the height of the emission region can lead to the change of the polarization position Angle. |
| Pages | 150 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/5158 |
| 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 | 孙盛楠. 脉冲星中爆发现象的研究[D]. 北京. 中国科学院大学,2021. |
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| 脉冲星中爆发现象的研究_孙盛楠.pdf（11301KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
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