活动星系核，作为宇宙中最明亮、持久的电磁辐射源，其观测特性主要依赖于以下几 点，如中心黑洞的质量、吸积率、吸积盘的取向、尘埃对核区的遮蔽程度，以及是否存在 喷流结构。基于这些观测性质，定义了多种活动星系核子类。对活动星系核的发现和研 究，有利于研究早期宇宙的结构和演化，并限制宇宙学模型。 本文主要针对耀变体在光学波段上的两种不同时标的光变特性进行了一系列研究。 耀变体作为活动星系核的一个子类，由中心1 ～ 100 亿个太阳质量的超大黑洞通过从 周围环境中以每年太阳量级质量的速率吸积物质来供能，从而产生以近光速向外运动的磁 化、高能等离子体喷流。喷流相对地球指向在10 度夹角以内，其中等离子体的超高速运 动产生多个相对论效应。耀变体具有贯穿整个电磁波段的非热连续辐射，存在高偏振和视 超光速运动现象，特别是其展现出了快速且强烈的光变特征。目前为止，仍没有确定的理 论模型来解释耀变体的这种光变现象。 在光学波段，耀变体具有显著的小时甚至分钟量级的快速光变。根据内秉机制，耀变 体天内光变可能来源于非常靠近中心黑洞的致密区域，或是喷流基部的最内部区域，或是 位于吸积盘的最内层。受到现有观测设备空间分辨率的限制，无法对耀变体喷流中的该致 密区进行直接成像观测。为了能更深入了解耀变体天内光变的辐射机制及理论模型，从而 对该辐射区域进行限制，我们利用三台反射望远镜主要对蝎虎天体的原型BL Lacertae 进 行光学多波段准同时性测光观测，通过分析其光变特征、颜色变化、波段间时间延迟等行 为，来深入探究其天内光变机制。研究发现，该源的各个观测波段之间具有很强的相关 性，并展现出显著的天内光变，具有很强的越亮越蓝的颜色行为，并且寄主星系对这种谱 行为影响不大，尤其我们在天内时标尺度上探测到长波领先短波约10 分钟的时延行为。 通过模型拟合，我们认为单一同步辐射脉冲理论可以很好的解释这种天内光变行为。 另一方面，目前的观测已覆盖全部电磁波段，一项重要的发现就是耀变体具有非常强 的伽马射线辐射（GeV 和TeV）。构建一个与射电、红外、X 射线和伽马射线等波段相对应 的光学长时标大样本观测数据库，是非常必要的。与此同时，耀变体的长时标光变与天内 光变的辐射机制和辐射区尺度不同。在长时标上，不同耀变体子类之间的光学特征具有明 显的差异性。为了进一步研究光学波段内部的长时标辐射机制，并探究对于不同耀变体子 类而言，各辐射成份对光学流量贡献的差异性，我们利用一台施密特望远镜对一批包含全 部耀变体子类的样本进行了6 年光学光变监测，精确追踪光变过程中的颜色变化，再结合 其他物理参量，研究耀变体长时标光变机制。该监测项目包括3 颗低频峰蝎虎天体、2 颗 中等峰蝎虎天体、4 颗高频峰蝎虎天体和1 颗平谱射电类星体，共收集了14799 个观测数 据点。除了OT 546 以外，所有目标源都展现了显著的光变特征。大部分蝎虎天体都具有 越亮越蓝的颜色行为，而平谱射电类星体，3C 454.3，则展现出越亮越红的颜色趋势。研 究发现长时标光变可由“强色变”的快速爆发＋“温和色变”的长时标光变这种双成份模 型来解释。低频峰蝎虎天体的平均谱指数大约为1.5，可以被同步自康普顿损失主导的模 型所解释。高频峰蝎虎天体可能受到来自寄主星系的热辐射污染。相关性分析并没有揭示 任何时间延迟的存在。 除此之外，我们研究发现耀变体的颜色行为不能简单的依靠耀变体的类别来划分，可 能与耀变体的光度也有关系。后续，我们将结合更多的观测数据，去判定是否存在光度阈 值这个因素影响耀变体的颜色行为。作为多颗耀变体源的最大光学样本的其中之一，未来 我们可以开展多波段相关性及能谱分析，从而进一步分析耀变体的各个辐射成份贡献及喷 流的最内部结构。

AGNs are the most luminous persistent sources of electromagnetic radiation in the universe. Their observed characteristics depend on several properties such as the mass of the central black hole, the accretion rate, the orientation of the accretion disk, the degree of obscuration of the nucleus by dust, and presence or absence of jets. Numerous subclasses of AGNs have been defined based on their observed characteristics. The discovery and study of AGN are conducive to the study of the structure and evolution of the early universe and to constraint on models of the cosmos. The analysis presented in this thesis is mainly to study the optical variability of two different timescales. Blazars, powered by black holes with masses of order 0.1-10 billion solar masses, are a subclass of active galactic nuclei (AGNs). The black holes are accreting material from their environment at rates of ∼1 solar mass per year. Such a system generally produces a pair of magnetized and high-energy plasma jets that flow outward from the center at near-light speeds. The jet points within about 10◦ to our line of sight, and the ultra-high velocity of the plasma results in some relativistic effects. Blazars are characterized by non-thermal radiation across the electromagnetic spectrum, as well as high polarization and apparent superluminal motions. In especial, their typical characteristics are fast and strong flux variability across the whole electromagnetic spectrum. Up to now, there is no definite theoretical model to explain these phenomena. In the optical band, blazar exhibits significant and rapid variations from hours down to minutes, often called intra-day variability (IDV). According to the intrinsic mechanism, IDV may originate from the dense region closed to the central black hole, or the innermost region at the base of the jet, or the innermost layer of the accretion disk. Due to the limited resolution of the existing facilities at high redshift, it is impossible to directly resolve the dense region. In order to discriminate different theoretical models on IDV and to constrain the radiation region in the jet, we use three reflectors to monitor BL Lacertae simultaneously at three optical wavelengths. By analyzing the characteristics of IDV, color behaviors and inter-band time correlation and lags, we can explore its IDV mechanisms. Our study found that the variations were well correlated at all wavelengths and the source showed significant IDV. A strong bluer-when-brighter (BWB) chromatism was found on the intra-day timescale. The spectral changes are not sensitive to the host galaxy contribution. Cross-correlation analysis revealed a possible time delay of about 10 mins between variations in the V and R bands. We interpreted the observed flares in terms of the model of individual synchrotron pulses. On the other hand, the universe can be observed by telescopes in every range of electromagnetic radiation. One important discovery for Blazar is its very strong gamma-ray radiations (especially in GeV and TeV). It is necessary to construct a large, long-term database in the optical regime. This database can be correlated to those in the radio, infrared, X-ray and gamma-ray bands. Meanwhile, the radiation mechanisms and spatial scales are different for the optical IDV and long-term variability of blazars. Different subclasses have distinct characters. In order to study the long-term radiation mechanism in the optical band and to explore the different contributions of each radiation component, we monitored a sample of blazars with all individual subclasses. We combine the accurate color variations with other physical parameters to explore their mechanisms. The monitoring project includes 3 LBLs, 2 IBLs, 4 HBLs, and 1 FSRQ. A total number of 14799 data points were collected. All objects showed significant variability except OT 546. Most BL Lac objects showed a BWB chromatism, while the FSRQ, 3C 454.3, displayed a redder-whenbrighter trend. Our researches suggest that the long-term variability can be interpreted in terms of two components: ”strong-chromatic” fast flares and ”mild-chromatic” long-term variations. The optical emission of HBL is probably contaminated by the thermal emission from the host galaxies. Correlation analysis did not reveal any time delay between variations at different wavelengths. In addition, our research shows that the color behaviors can not be simply classified by subtypes of blazars. It may also be related to the luminosity. We will use more observation data to determine whether there is a luminosity threshold which affects the color behaviors of blazars. As one of the largest optical databases for a sample of blazars, it can be used to develop the multiwavelength variabilities and SED analysis, and to further analyze the contribution of various radiation components and the most inner structure of the jet.