KMS of Xinjiang Astronomical Observatory, CAS
| 射电脉冲星辐射变化研究 | |
| Alternative Title | Emission variation study of radio pulsars |
王双强
| |
| Subtype | 博士 |
| Thesis Advisor | 王娜 ; 王晶波 |
| 2021-06-01 | |
| 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 射电脉冲星 间歇脉冲星 毫秒脉冲星 |
| Abstract | 射电脉冲星通常表现出多样的辐射变化，例如模式变换，消零和周期性辐射调制等现象。间歇脉冲星是一种特殊的脉冲星消零现象，其辐射消失的时标从几天到几个月，甚至几年，观测特性表现为``on''态的能损率大于``off''态。它们的发现使我们能够首次计算脉冲星磁层中的粒子密度，这对脉冲星辐射物理研究至关重要。我们使用澳大利亚Parkes射电望远镜对两颗间歇脉冲星 (PSR J1832+0029和J1841-0500) 长时间监测，并进行后续研究。PSR J1832+0029和J1841-0500是两颗长时标的间歇脉冲星，其on-off循环时标在年量级。对于PSR J1832+0029，我们在``off''态探测到了一次辐射，这表明间歇脉冲星可能存在短时标的on-off转换。对于PSR J1841-0500，我们长时间跨度的观测表明其on-off循环并不是准周期性，这与所发现的第一颗间歇脉冲星不同。通过单脉冲分析，我们发现该脉冲星在``on''态的辐射呈现出周期性的振幅调制，这是第一颗表现出振幅调制的间歇脉冲星。双中子星系统可以用于约束爱因斯坦的引力理论。PSR B1534+12 在0.7%的精度上证明了爱因斯坦引力理论的正确。通过分析FAST的观测数据，我们发现 PSR B1534+12表现出两种不同的辐射态：弱态和爆发态。弱态辐射一直存在，其脉冲轮廓较宽，能量满足高斯或者对数正态分布；爆发态脉冲轮廓较窄，能量较强，其中最亮脉冲的峰值强度比平均脉冲高334倍，其脉冲能量满足幂律分布。此外，弱态与爆发态的平均脉冲轮廓表现出不同的偏振性质。我们的结果表明PSR B1534+12的两种辐射态产生于脉冲星磁层的不同位置。我们进一步探究爆发态脉冲对计时的影响，发现仅选择爆发态脉冲虽然可以显著降低到达时间不确定度，但是与所有脉冲相比并没有提高计时精度。我们把原因归结于爆发态脉冲的jitter噪声较大，并对jitter进行量化。毫秒脉冲星是不同于常规脉冲星的另一类脉冲星，其辐射通常比较弱。我们使用高灵敏度的FAST望远镜对一些毫秒脉冲星进行观测，以研究其辐射变化。PSR J0621+1002是一颗被长时间监测用于低频引力波探测的毫秒脉冲星。我们的单脉冲分析表明该脉冲星的辐射存在明显的周期性变化。通过波动谱分析，我们发现其第一个和第三个脉冲成分周期性振幅调制现象，而第二个成分比较稳定，其中第一个脉冲成分的振幅调制周期为3.0个脉冲周期，而第三个脉冲成分的振幅调制比较弥散，主要集中在3.0和200个脉冲周期。通过对单脉冲计时研究我们发现PSR J0621+1002的计时残差分为很明显的两部分，称为模式A和模式B，其中A为主导模式。但是这并不是传统的模式变换现象，因为模式B并不稳定。通过对模式A和模式B的单脉冲进行单独的计时研究，我们发现单独选择不同模式的单脉冲并不能提高计时精度，此外，选择高信噪比的单脉冲进行计时同样不能能提高计时精度。PSR J1720-0533是FAST-CRAFTS巡天发现的毫秒脉冲星双星，属于黑寡妇，特点是存在射电掩食。我们使用FAST望远镜对这颗脉冲星进行后续观测，研究其掩食前后辐射的变化。我们发现PSR J1720-0533的掩食前后的辐射并不对称，进入掩食过程中，脉冲星辐射表现为周期性的强度变化，调制周期约为26 s，出掩食过程中，辐射表现为突然增强，并没有探测到类似的周期性辐射变化。这也是首颗在进入掩食过程中探测到周期性辐射变化的黑寡妇，具体的物理机制仍不清楚。模式变换是指脉冲星的辐射在两个或多个稳定状态之间切换，其物理原因仍不清楚。我们使用澳大利亚Parkes望远镜的超宽带接收机 (带宽704-4032 MHz) 对七颗模式变换脉冲星进行偏振观测。通过偏振分析，我们把模式变换分为三类：(1) 不同态的线偏振位置角相同，包括PSR J0922+0638，PSR J1048-5832，PSR J1326-6700, PSR J1822-2256和PSR J1825-0935，其中PSR J0922+0638两个态的谱指数相同，其余谱指数均不同，其不同态的磁层结构保持不变，模式转换可能是磁层中粒子流的变化引起加速区辐射变化导致；(2) 不同态的线偏振位置角不同，包括PSR J0941-39，其两个态的谱指数不相同，其态转换可能是磁层结构的改变导致的；(3) 不同态的线偏振位置角不同但其中某个态一直存在，包括PSR J1938+2213，其弱辐射态一直存在，爆发态的偏振性质明显不同于弱态，两个态的谱指数同样不同，我们认为爆发态产生于磁层中不同于弱态的位置，但是磁层结构没有变化。不同模式变换的物理起源可能不同。 |
| Other Abstract | Radio pulsars are known to exhibit various emission properties, such as the pulsar nulling, mode changing and periodical emission variations. The intermittent pulsar is a special type of nulling pulsar, in which the emission suddenly shuts off with the duration time from several days to years. The discovery of the intermittent pulsar allows us to estimate the magnetospheric currents in a pulsar magnetosphere during the occurrence of radio emission for the first time. We present long-term observations of two intermittent pulsars, PSRs J1832+0029 and J1841-0500 using the Parkes 64 m radio telescope. The radio emission for these pulsars switches ``off'' for year-long duration. Our new observations have enabled us to improve the determination of the on-off timescales and the spin down rates during those emission states. Weak emission was detected in an observation of PSR J1832+0029 during an ``off'' emission state. For PSR J1841-0500, we also found that the on-off cycle time of PSR J1841-0500 is not quasi-periodical. We also identified a quasi-periodic fluctuation in the intensities of the detectable single pulses, with a modulation period between 21 and 36 pulse periods.Double neutron systems provide rigorous tests of Einstein's general theory of relativity. PSR B1534+12 is valuable tool to test GR and confirmed GR at the 0.7% level. We have observed PSR B1534+12, a pulsar with a neutron star companion, using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We found that this pulsar shows two distinct emission states: a weak state with a wide pulse profile and a burst state with a narrow pulse profile. The weak state is always present. We cannot, with our current data, determine whether the pulse energy of the weak state follows a normal or a log-normal distribution. The burst state energy distribution follows a power-law. The amplitude of the single pulse emission in the burst state varies significantly; the peak flux intensity of the brightest pulse is 334 times stronger than that of the average pulse. We also examined the timing precision achievable using only bright pulses, which showed no demonstrable improvement because of pulse jitter and therefore quantified the jitter noise level for this pulsar.The emission variations of millisecond pulsars are difficult to detect because of their low flux densities. Using the FAST, we presented a radio observation of a millisecond pulsar PSR J0621+1002 which is monitored by the European Pulsar Timing Array. The pulsar shows periodic pulse intensity modulations for both the first and the third pulse components, whereas, no modulations in the pulse phase are found. The fluctuation spectrum of the first pulse component has one peak of 3.0 pulse periods, while that of the third pulse component has two diffused peaks of 3.0 and 200 pulse periods. The timing residuals of the single pulsars are divided into two class which are named mode A and mode B, respectively. However, this is not the typical mode change because the mode B is not stable. We examine the timing precision achievable using only pulses in one mode or bright pulses, and found that the timing precision improvement is not achievable. PSR J172-0533 is a binary millisecond pulsar with a 3.26 ms spin period and 3.16 hr orbital period, which was discovered in FAST CRAFTS survey. The pulsar belongs to black widow and radio eclipses are detected. Our high sensitive observation provides great detail on the emission variations near the eclipse of PSR J1720-0533 using FAST. We found that there is a quasi-periodic pulse emission modulations during the ingress of the eclipse of this pulsar with a modulation period of 26s. No such modulation was found during the egress of the eclipse. The physics origin of this phenomenon is unclear.Mode changing is kind of discontinuous change in which pulse profile switches between two or more stable states. The UWL receiver installed on Parkes radio telescope allows us to study the the mode switch pattern in a wide frequency range of 704-4032 MHz. Using the UWL receiver, we observed seven mode changing pulsars. By analyzing the polarization properties and the spectrum of different modes for each pulsar, we found that these pulsars can be divided into three class: (1) the linear position angles of different modes are similar, including PSR J0922+0638, PSR J1048-5832, PSR J1326-6700 PSR J1822-2256 and PSR J1825-0935. The spectrum indexes of the two modes for PSR J0922+0638 are same, while those for other pulsars are different. We suggested that the magnetosphere geometries in different modes are different for this pulsar class and attributed the mode changing to the different distributions of currents. (2) the linear position angles of different modes are different, including PSR J0941-39. The spectrum indexes of the two modes for this pulsar class are different. We attributed the mode changing to the change of pulsar magnetosphere geometries. (3) The linear position angles of different modes are different and one mode is always present, including PSR J1938+2213. The weak mode of PSR J1938+2213 is always present and the spectrum indexes of the weak and burst mode are different. We suggested that the magnetosphere geometries are not changed and the emission for the two modes is generated in two different regions in the pulsar magnetosphere. Different mode changing may have different physics origins. |
| Pages | 158 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/4735 |
| 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 | 王双强. 射电脉冲星辐射变化研究[D]. 北京. 中国科学院大学,2021. |
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| 射电脉冲星辐射变化研究_王双强.pdf（24410KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
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