Blazar天体高能辐射与河外背景光
文献类型：学位论文
| 作者 | 杨建平 |
| 学位类别 | 博士 |
| 答辩日期 | 2010-05-27 |
| 授予单位 | 中国科学院研究生院（云南天文台） |
| 授予地点 | 北京 |
| 导师 | 王建成 |
| 关键词 | Blazar天体 辐射机制 体速度结构 河外背景光（EBL） 正负电子对产生 |
| 学位专业 | 天体物理 |
| 中文摘要 | 通常，人们使用简化的一维均匀喷流模型来解释AGN的观测。但这样的简化面临较大的观测矛盾，不同波段的观测表明，喷流应该具有体速度结构。我们构造了具有连续横向和纵向体速度结构的喷流模型，包括了同步自康普顿模型（SSC）和外康普顿模型（EC）。对于不同的视角和速度结构，体速度结构对观测谱的影响表现出复杂而独特的性质。具有体速度结构的SSC和EC模型被我们用来讨论Mrk 421，0716+714和3C 279的观测，讨论了BL Lac天体和FR I天体的统一模型。体速度结构在不同视角下，对于观测谱的影响差异很大。除了视角，体速度结构对BL Lac天体与FR I天体统一模型也有较大影响。同时，我们也用具有体速度结构的EC模型讨论了FSRQ与FR II的观测谱，我们发现体速度结构对于EC模型的影响比对SSC的影响小得多。 最近，观测到了一些IBL（如W Comae 和 3C 66A ），LBL（BL Lacertae）甚至FSRQ（3C 279）有非常高能（VHE）的辐射。这些天体的VHE辐射引起了人们极大的关注。3C 66A的Fermi观测（0.2-100GeV）表现出较平的光子谱指数$\Gamma$=1.97），而准同时的能量略高的VERITAS观测（200-500GeV）退吸收后则出现了较硬的光子谱指数（$\Gamma$=1.1），这很难用单一的辐射模型对这些高能的观测作出合理的解释。我们的解释是：（1）、退吸收谱强烈依赖于红移，如果z=0.444，可以用SSC成分来解释Fermi观测；而VERITAS观测用EC模型来解释。这也表明了在IBL的高能观测中很可能出现EC成分，这些EC成分能够达到几百GeV的量级。（2）、如红移是0.1，Fermi谱和VERITAS谱变为一个平滑连接，用一个SSC模型就能解释高能观测，这也许表明了该天体的红移小于0.444。 远距离的VHE光子到达观测者的过程中将不可避免受到低能光子（如来自河外背景光，EBL）的碰撞，产生正负电子对。我们可以通过这样的吸收特性，利用Blazar的VHE观测来间接研究EBL。 EBL的研究和Blazar高能辐射的研究相辅相成，相互促进。我们利用了最新的Blazar的TeV观测来研究EBL，给出EBL能谱的一些上限，为EBL的理论模型提供帮助。 BL Lac天体通常缺乏发射线和吸收线，因此一些BL Lac天体的红移很难确定，我们通过研究高能伽玛光子与EBL的相互作用来对三个BL Lacs天体的红移给出限制。 |
| 英文摘要 | The simple one-zone homogeneous jet model usually provides a good framework to explain the emissive spectra of AGN jets. However, it is argued that the jet should have velocity structures to mediate the inconsistence of bulk motions obtained by different wavebands. The synchrotron self-Compton (SSC) models and External Compton (EC) models of AGN jets with continually longitudinal and transverse bulk velocity structures are constructed. The observed spectra show complex and interesting patterns in different velocity structures and viewing angles. These models are used to calculate the synchrotron and inverse Compton spectra of two typical BL Lac objects (BLO) (Mrk 421 and 0716+714) and one Flat Spectrum Radio Quasars (FSRQ) (3C 279), and to discuss the implications of jet bulk velocity structures in unification of the BLO and FR I radio galaxies (FRI). By calculating the synchrotron spectra and SSC spectra of BL Lac object jets with continually bulk velocity structures, we find that the spectra are much different from ones in jets with uniform velocity structure under the increase of viewing angles. The unification of BLO and FR I is less constrained by viewing angles and would be imprinted by velocity structures intrinsic to the jet themselves. Finally, we present the EC spectra of FSRQ and FR II radio galaxies (FR II) and find that they are weakly affected by velocity structures compared to synchrotron and SSC spectra. Nowadays, IBL (W Comae and 3C 66A), LBL (BL Lacertae), and FSRQ (3C 279) display the potential to emit at VHE energy band, which attract great deal of attention upon them. We model the high-energy spectrum of 3C 66A, which was observed recently with the Fermi-LAT and VERITAS telescopes. The spectrum has a hard change from the energy range of 0.2-100 GeV to 200-500 GeV in recent almost contemporaneous observations of two telescopes. (1) The de-absorbed VERITAS spectrum depends strongly on redshift, which is highly uncertain. If z=0.444 is adopted, we are able to use the SSC model to produce the Fermi-LAT component and the EC model to the VERITAS component. For the VHE observations of IBL, EC component might be observed. (2) However, if z=0.1, the intrinsic VERITAS spectrum will be softer, and there will be a smooth link between the Fermi-LAT and VERITAS spectra that can be explained using an SSC model. It might indicate that the redshift of this source is less than 0.444. The VHE photons will be absorbed by the extragalactic background light (EBL) through pair production. Absorption features imprinted on the $\gamma$-ray spectra of distant blazars by background light photons provide an indirect approach to study the EBL. The research of VHE emission of blazars and EBL could promote mutually. The upper limits on the EBL, using the TeV spectra recently observed in TeV blazars, are presented. BL Lac objects usually present no or weak emission lines, and their redshifts are not easily determined. Comparing the measured and intrinsic VHE spectra due to EBL absorption, we give the redshift upper limits of three blazars. |
| 学科主题 | 天文学 |
| 语种 | 中文 |
| 页码 | 132 |
| 源URL | [http://ir.ynao.ac.cn/handle/114a53/5083]  |
| 专题 | 云南天文台_高能天体物理研究组 |
| 推荐引用方式 GB/T 7714 | 杨建平. Blazar天体高能辐射与河外背景光[D]. 北京. 中国科学院研究生院（云南天文台）. 2010. |
入库方式： OAI收割
来源：云南天文台
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