Blazar 喷流的高能辐射模型以及外光子场的研究
文献类型：学位论文
| 作者 | 高小燕 |
| 学位类别 | 博士 |
| 答辩日期 | 2011-05-26 |
| 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 喷流 辐射机制 红外背景辐射 外光子场 |
| 其他题名 | Research of High Energy Radiation and external field of Jets in Blazars |
| 学位专业 | 天体物理 |
| 中文摘要 | Blazar高能辐射的产生机制存在着争议，目前有不同的辐射模型对其进行解释。TeV blazars的甚高能γ射线爆发通常情况下会伴随着X射线爆发，然而2002年观测到的1ES 1959+650“孤立”的闪耀（γ射线爆发的过程没有X射线闪耀伴随）对均匀单一的SSC模型提出了巨大的挑战。另外近期的一些观测发现γ射线与X射线的相关性很差，表明它们的光子可能来自于不同的辐射区。我们给出一种新的模型，认为高能辐射来自于内区质子的同步辐射过程，而低能辐射来自于外区电子的同步辐射过程。模型的图景是这样的：喷流中抛出一个致密的物质团，在离黑洞很近时含有大量的高能粒子，包括质子和电子，此时磁场很强，高能质子在强磁场下会以同步辐射产生高能γ射线光子。而物质团中的电子的同步辐射产生的光子会被致密的物质所吸收掉。当物质团继续膨胀时，密度降低，磁场减弱，而此时光子因为湮灭过程而产生的电子数目增加，物质团与外界物质相互碰撞产生激波，加速这些电子；它们通过同步辐射产生观测到的低能辐射。由于高能和低能的光子来自于两个不同的区域，能够解释不同波段之间的非相关性和孤立爆发的情况，而且降低了对较大多普勒因子的要求。对于具有多普勒集束效应的TeV blazar，我们基于均匀的SSC辐射能谱的高能和低能成分来对多普勒因子进行估算。高能端的谱由于受到河外背景光（intergalactic background light，IBL）吸收的影响而改变谱型，我们对其进行了修正。利用多波段的数据估计了8个TeV blazar的多普勒因子和γ射线光深。发现一部分源具有合适的Doppler因子以及比较大的光深，这表明电子对的产生过程是不可避免的。但是对于H 1426+428和PKS 2155-304两个源的Doppler因子的值却很大，均匀喷流模型在解释γ射线辐射过程中存在困难。外康普顿辐射模型被广泛地应用于解释一些blazar的高能辐射，而外光子场的性质又是决定外康普顿散射重要的参数。我们通过研究FERMI-LAT望远镜前三个月观测到的亮AGN样本的能谱来约束外光子场。假设低同步峰频blazar样本的高能辐射全部来自于外康普顿辐射的贡献，我们发现外光子场 的参数Uext/νext不是常数。通过准同时性观测得到的能谱来计算同步和逆康普顿光度，发现它们之间存在近似的线性关系。这表明在共动系中外光子场能量密度和磁场的能量密度之间也存在着线性的关系，因此高能辐射区的洛伦兹因子依赖于外光子场和磁场。这个结论对喷流的动力学给出了强烈的约束。 |
| 英文摘要 | There exist a big dispute of the high energy emission of AGNs. Many models have been given to explain the radiation. Very high energy γ−ray flares of TeV blazars are generally accompanied with simultaneous active X-ray flares. However the observation of an “orphan” TeV flare of 1ES 1959+650 in 2002(without a simultaneous X−ray flare) is a challenge to standard leptonic synchrotron self-Compton (SSC) model. In addition the recent observation showing the loose correlation between X−ray and TeV γ−ray means that these two energy band photons may not emitted in the same regime, which also conflicts with SSC model. Here we give another model. We assume that high energy emission is produced by the accelerated protons in an inner blob near the black hole with a large magnetic field, while the low energy radiation comes from the electrons in the expanded blob. Under this situation the “orphan” TeV flares and the loose correlation between different energy band can be explained easily. Because the high and low energy photons are not produced in the same region, the requirement of large Doppler factor from pair production is relaxed. We present the estimations of the beaming Doppler factor in TeV Blazars based on the synchrotron self-Compton (SSC) uniform models from the observed low and high energy spectra. Using the high energy spectra corrected from the absorption of the intergalactic background light (IBL), we estimate the Doppler factors and the optical depths of gamma-ray absorption for eight TeV Blazars with multiwavelength data. We found that some sources have the modest values of Doppler factor and large optical depths. It implies that pair production is not avoidable. The high values of the Doppler factor appear in two objects of H 1426+428 and PKS 2155-304. It means that the uniform jet model faces difficult in explaining gamma-ray emission. The external Compton (EC) model is used to study the high energy emission of some blazars, in which the external photon field is considered to dominate inverse Compton radiation. We explore the properties of external photon field through analyzing the FERMI LAT bright AGN sample within three months detection. In the sample, assuming the high energy radiation of low synchrotron peaked blazars from the EC process, we find that the external photon parameter Uext/νext may not be a constant. Calculating synchrotron and inverse Compton (IC) luminosity from the quasi-simultaneous broadband spectrum energy distributions (SEDs), we find that they have an approximately linear relation. This indicates that the ratio of external photon and magnetic energy density is a constant in the comoving frame, implying that the Lorentz factor of the emitting blob depends on external photon field and magnetic field. The result gives a strong constraint on the jet dynamic model. |
| 学科主题 | 天文学 |
| 语种 | 中文 |
| 公开日期 | 2016-05-03 |
| 页码 | 104 |
| 源URL | [http://ir.ynao.ac.cn/handle/114a53/5089]  |
| 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 | 高小燕. Blazar 喷流的高能辐射模型以及外光子场的研究[D]. 北京. 中国科学院研究生院（云南天文台）. 2011. |
入库方式： OAI收割
来源：云南天文台
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