| 摘要 | 耀变体（blazar）是一类性质奇特的活动星系核（AGN），剧烈光变和高偏振是其定义特征。耀变体都是射电噪活动星系核，其连续谱辐射以非热辐射为主，都具有射电喷流，并且喷流具有视超光速运动。这些观测特征通常采用相对论喷流模型来解释，即喷流运动速度是相对论性的，并且运动方向与我们观测者视线方向的夹角小,从而产生多普勒放大效应。耀变体是研究宇宙中非热辐射机制，喷流产生、加速与准直等天体物理基本问题的理想天体。光变和偏振特性的观测研究是解决这些基本问题的重要途径，同时也一直是耀变体研究的重要内容。本论文针对耀变体的光变与偏振特性开展观测研究，主要创新成果如下：（1）偏振测量是研究 AGN 喷流磁场结构和同步辐射机制的重要手段, 但我国一直没有可以开展光学偏振测量的相关科学仪器。针对这一现状，我们系统调研了世界上多个著名通用光学望远镜配备的偏振测量仪器, 根据它们的优缺点和发展现状，结合丽江 2.4 米望远镜及其卡焦科学仪器 YFOSC(云南暗弱天体光谱成像仪) 的自身特点，我们研制了两套偏振测量系统：单光束调制模式的线偏振仪器 YFPOL 和基于双沃拉斯顿棱镜(WeDoWo) 的同步偏振仪器。虽然 YFPOL是一套基于偏振片旋转调制的传统偏振计，但我们首次实现了该偏振调制系统在超薄尺寸 (总厚度小于 12mm) 上高精度 (定位精度优于 0.01 度) 的双无线控制(无线供电和无线控制)，同时采用了超高消光比（1,000,000:1）偏振片，从而保证了 YFPOL 的优异性能。另外我们还详细分析了 YFPOL 全视场 (7′ × 7′) 内的仪器偏振特征，设计了大幅降低仪器偏振误差的数据处理方案，并基于该方案开发了数据处理软件。通过对多颗偏振标准星的定标观测，得到了 YFPOL 的偏振度测量误差（<0.8%）和偏振角修正值 (2.6∘)。YFPOL 的成功研制，为开展耀变体及其他天体的偏振观测研究奠定了坚实基础。另外，我们还根据 2m4 和 YFOSC的光学系统参数研制并实现了基于 WeDoWo 的同步偏振计，通过一次曝光就可完成线偏振测量。但是由于 YFOSC 本身的光学系统限制，暂时还无法使用该仪器开展常规的偏振观测，详见章节4.4.3。同步偏振调制是未来高精度偏振测量仪器的发展方向，我们正计划研制双同步 (同步偏振调制和多色同步)、高时间分辨率 (冻结大气曝光) 的下一代高精度偏振仪器。（2）我们使用 YFPOL 分别对耀变体 S5 0716+714 和 PKS 0735+178 开展了多波段偏振监测工作。S5 0716+714 是一个被广泛观测和研究的蝎虎天体，但是关于该目标的偏振特性研究仍然较少。我们对该目标进行了长时间（106 天）的双波段（𝑉 波段和 𝑅 波段）偏振监测，通过 YFPOL 的偏振观测结果，总结其偏振特性如下：S5 0716+714 长期处于高偏振 (>6%) 状态，且偏振度在不断变化，并伴随有短期的低偏振状态（10 天内偏振度<3.5%）。发现了其偏振角的长期旋转现象和短期的大幅摆动>100∘) 现象。我们的观测结果与 Marscher 等人提出的喷流中极多湍流单元 (TEMZ) 模型预测的结果一致。另外，我们还观测了IceCube-211208A 预警的中微子成协耀变体目标 PKS 0735+178, 结果显示该目标在光学流量上存在显著的变暗过程 (SDSS𝑖 波段下降了一个星等)，但是偏振度却具有明显的上升过程 (SDSS𝑖 波段的偏振度从 4.7% 上升至 13.6%)，偏振角呈现小幅摆动现象 (变化幅度 < 20∘)。同时，我们还对比了两个目标测光光度与偏振光度的变化曲线，发现二者存在高度一致性，这说明在偏振采样周期内目标光度比较稳定，也间接说明了偏振数据的可靠性。（3）我们使用 YFOSC 对 𝛾-ray 窄线塞弗特 1 星系 PMN J0948+0022 进行了长期的多色测光和光谱观测。通过对光变数据的 𝐹 检验和 ANOVA 方差分析，我们在两个观测夜中探测到 𝑅 波段的日间光变（IDV）现象，光变占空比为 29%,光变幅度大于 12.9%，说明该目标辐射中包含相对论性喷流的成分，与耀变体的观测特征一致。另外，我们还发现该目标在不同时间尺度上均存在变亮变红(RWB)的颜色变化趋势，而当目标亮于 𝑅 = 17.5mag 时，该特征消失，说明此时喷流非热辐射成分与吸积盘的热辐射成分对目标光度的贡献相同，即各占 50%。在光谱数据处理时，我们利用光谱观测时的 𝑅 波段星等与拐点星等 (𝑅 = 17.5mag) 之间的比值，有效的扣除了喷流对单波长光度的影响，进而得到了吸积盘在 5100Å处的有效光度 𝐿5100。然后利用 R-L 关系和维里方程得到了黑洞质量𝑀• = 1.61 × 107𝑀⊙，进而得到了吸积率ℳ = 93，确认了 PMN J0948+0022 是一个超爱丁顿吸积的 AGN。 |
| 其他摘要 | Blazars are a class of active galactic nuclei (AGNs) with observational properties include: very high luminosity, a two-hump shaped SED dominated by the nonthermal emission, strong variability and a high polarization degree from radio to optical. These peculiar phenomena are generally explained by the relativistic jet model, the jets have relativistic speed, superluminal motion and directed close to our Line-of-Sight (LOS). The study of optical variability and polarization are important windows to probe the mechanism of synchrotron radiation and the magnetic field topology of blazar.(1) Polarimetry plays an important part in studying the nature of the AGN jet. but there is no night astronomical polarization instrument in China. As a result, We developed two sets of polarization measurement systems integrated with Yunnan Faint Object Spectral Imager (YFOSC) on lijiang 2.4-m telescope (LJT): linear polarization instrument YFPOL with single beam modulation mode and synchronous polarization mode with double Wollaston prism (WeDoWo). YFPOL is a traditional polarimeter with rotating polarizer, which have characteristics include: ultra-thin (thickness<12mm), high precision (positioning accuracy < 0.01∘), wireless control and charging functions and high extinction ratio (1,000,000:1) polarzer. We also analyzed the polarization characteristics of the YFPOL in the full field of view (FOV, 7′ × 7′), and give a data processing scheme to minimize the instrumental polarization error. Based on this scheme, we developed the pipeline for YFPOL. Finally, we obtain the uncertainty of polarization degree (<0.8%) and offset of polarization angle (2.6∘) of YFPOL by calibration of zero-polarized and highly-polarized standard stars. In addition, we have designed and tested a synchronous polarization instrument based on WeDoWo, due to the specialoptical system of YFOSC, the scheme has many observation limitations (see section 4.4.3). We have temporarily abandoned the polarization monitoring work based on this scheme.(2) We conducted multi-band polarization monitoring based on YFPOL for blazar S5 0716+714 and PKS 0735+178. S5 0716+714 is a widely observed and studied BL Lac object, but its polarization characteristics are not well studied. We performed a long period (106 days) of polarization monitoring on 𝑉 -band and 𝑅-band, obtained 78 𝑉 -band data (two intra-night polarization data) and 39 𝑅-band data. The polarization characteristics are summarized as follows: S5 0716+714 has a high polarization degree (PD>6%) in long timescales, along with short-term lower state (PD<3.5% 10="" within="" .="" long-term="" rotation="" of="" electric="" vector="" position="" angle="" and="" short-term="" polarization="" degree="" swing="" pa="">100∘) are found. Our observations are in agreement with Alan Marscher’s TEMZ model in jet. In addition, we also observed the neutrino candidate target PKS 0735+178, which was alert by IceCube-211208A. Observations show that the luminosity dropped by one magnitude, but PD increased from 4.7% to 13.6% with small rotation of EVPA (< 20∘) on SDSS𝑖-band. We also compared the variability of photometry and polarimetry, the two are consistent, which indicates that the target is stable during the polarization observation, and indirectly proves the reliability of the polarization data.(3) In order to study the physical properties of the 𝛾-ray emitting narrow-line Seyfert1 (NLS1) galaxy population, photometric and spectral observations of the 𝛾-ray emitting NLS1 PMN J0948+0022 were made with the Lijiang 2.4 m optical telescope. Photometric data in the 𝐵 and 𝑅 bands were collected for 50 nights from 2020 January to 2021 December. During the observation epoch, the variability amplitudes are 73.67% in the 𝐵 band and 79.96% in the 𝑅 band. Intra-day variability is found in two observation nights, and the duty cycle value is 29% with variability amplitude > 12.9% in the 𝑅-band, which support the presence of the relativistic jets in the target. The redder-when-brighter (RWB) chromatic trend appears on intra-day and long timescales. The RWB trend is dominated by the radiation of accretion disk and jet, and resembles those in flat spectrum radio quasars. When PMN J0948+0022 is brighter than 17.m5 in the 𝑅 band, there is no color change trend. By analyzing the spectral data of PMN J0948+0022, we obtained the black hole mass of 𝑀• = 1.61 × 107𝑀⊙ and accretion rate of ℳ = 93, and confirmed that PMN J0948+0022 is a super Eddington accreting NLS1. |
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