Blazar高能辐射研究

题名	Blazar高能辐射研究
作者	雷买昌
学位类别	博士
答辩日期	2015-07-01
授予单位	中国科学院研究生院
授予地点	北京
导师	王建成
关键词	活动星系核耀变体平谱射电类星体蝎虎天体
其他题名	Researches on high-energy radiations to blazar
学位专业	天体物理
中文摘要	Blazar（耀变体）是一类极端的活动星系核（AGN），根据宽发射线强弱划分为平谱射电类星体（FSRQ）及蝎虎天体（BL Lac），很多证认的河外$\gamma$射线源都属于这一类。由于它们产生的相对论喷流近乎指向观测者的视线方向，产生的非热辐射由于多普勒效应而显著增亮，使它们成为我们研究河外天体吸积、加速机制、喷流构成、喷流中粒子与粒子间、粒子与光子间，以及喷流与外部绕核物质相互作用的重要窗口。因此，对blazar的研究成为当今天文学中的一个极其活跃的研究领域。在轻子模型框架下，BL Lac天体喷流内的相对论粒子散射自身产生的同步辐射光子形成观测到的GeV到TeV谱。对于FSRQ天体，观测到的GeV光子来源于相对论电子对外部软光子的散射，这些光子就源自宽线区（BLR）或是尘埃环（dust torus），这种框架能够很好地解释FSRQ天体的多波段能谱及X射线与$\gamma$射线间的相关性，但面临的问题是当辐射区位于BLR空腔内部时，如何降低BLR光子场对GeV光子的吸收，因为在这种条件下，几十个GeV能段以上的$\gamma$射线光子将遭受$\gamma+\gamma \to e^{\pm}$过程，很难避免被吸收的命运。因此，我们提出``扁平"的BLR结构，扁平度由倾角$\alpha$来衡量。在这种结构下，BLR产生的能量密度是$\alpha$的函数。这样，即使辐射区位于BLR空腔以内，在较低的$\alpha$及特定位置处，FSRQ天体产生的所有光子都能够逃逸出宽线区辐射辐射场。此外，我们收集了3C 454.3在2007年7月至2011年1月准同时性的多波段能谱，应用吸积盘、尘埃环及一个``平"的宽线区结构来解释$\gamma$射线外暴。在模型中，低能成分来源于相对论电子的同步辐射，高能成分由两个峰构成，将分别由康普顿散射尘埃环和BLR光子来产生。我们的结果表明：（i）BLR的倾角大约在$45^{\circ}$附近；（ii）在外暴期间，喷流由物质主导；（iii）对于3C 454.3现有的两个黑洞质量的值：$5\times 10^{8}$\,$M_{\odot}$ 和$4.4\times 10^{9}$\,$M_{\odot}$，我们的模型认为前者可能性更大。 Mrk 501是一个典型的BL Lac天体，2009年Fermi协同其它能段的望远镜对其进行了一次多频监测，首次获得了较为完整的多波段能谱。在单区均匀SSC模型下，很难对多波段数据给出一个满意的拟合。谱及流量分析也表明它的辐射区性质更加复杂，在这样的背景下，我们提出双区均匀SSC模型解释，在这种框架下，我们能够满意的拟合多波段能谱，同时也能够对其中的加速机制给以限制，结果表明扩散激波加速在基态扮演一个重要作用，而暴发态可能是一系列预加速机制共同作用的结果。
英文摘要	Blazars is an extreme class of active galactic nuclei (AGNs), which is divided into BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs), according to the intensity of observed broad-emission lines. Most extragalactic objects identified in $\gamma$-rays belong to this category. Owing to their relativistic jet pointing aligned with the line of sight, the non-thermal radiations produced will dramatically be Doppler-boosted. It has been the window to explore the matter accretion, acceleration mechanism, jet content and the interactions between particles and particles or particles and photons, together with jet and circumnuclear matter. Therefore, the investigations on blazars has been an active area in modern astrophysics. Under the framework of the leptonic models, the spectrum from GeV to TeV band originates from Compton scattering of local photons by relativistic electrons for BL Lacs. Whereas for FSRQs, the observed GeV photons come from Compton scattering of external soft photons, those photons could come from broad-line region (BLR) or dust torus, such framework can satisfactorily explain the spectral energy distributions (SEDs) and correlation between X- and $\gamma$-rays. But we have to solve the problem: how to reduce the absorption to GeV photons when the emission region is located within the cavity of the BLR? Under the context of spherical BLR structure, the $\gamma$-rays photons with energies above tens of GeV will suffer from $\gamma+\gamma \to e^{\pm}$ processes, and cannot avoid the fate of absorption. Therefore, we propose a BLR model with ``flat" structure measured by aperture angle $\alpha$. Under such structure, the energy density of the BLR is the function of the radial distance. So that, almost all of the photons originating from the emission region can escape the diffuse photon field of the BLR, even if the emission region located within the cavity of the BLR. Moreover, we collect the quasi-simultaneous SEDs of 3C 454.3 obtained by the multi-wavelength campaigns in 2007 July to 2011 January, and use a model with the ``flat" structure BLR, accretion disc and dust torus to explain the SEDs of gamma-ray outbursts. In the model, the low-energy component would come from the synchrotron radiation of relativistic electrons and the high-energy component consists of two humps would be produced by the synchrotron self-Compton (SSC) and external Compton (EC) processes, in which the first hump peaking at X-rays would be produced by the SSC emission, the second one peaking at GeV $\gamma$-rays would come from the Compton scattering of dust torus and BLR radiations. We obtain the following results: (i) The aperture angle $\alpha$ describing the BLR structure is about $45^{\circ}$; (ii) The jet is almost dominated by the matter during the outbursts; (iii) The central black hole (BH) mass is about $5\times 10^{8}$\,$M_{\odot}$ rather than $4.4\times 10^{9}$\,$M_{\odot}$. Mrk 501 is a typical BL Lac. In 2009, Fermi and other telescopes carried out a multifrequency campaign, obtained a complete SED. However, those SED data cannot fit well by one-zone homogeneous SSC model. The analysis related to the spectrum and flux suggested that the properties within the emission region is more complex. Under such arguments, we propose another explanation related to two zones. Such that we can satisfactorily reproduce SED . Meanwhile, it can impose some constraints on acceleration mechanism. The result show that the diffusive shock acceleration mechanism could play an important role in baseline state, while the flaring state, may be a result of multiple pre-acceleration mechanism.
语种	中文
学科主题	天文学
内容类型	学位论文
源URL	[http://ir.ynao.ac.cn/handle/114a53/5101]
专题	云南天文台_高能天体物理研究组
作者单位	中国科学院云南天文台
推荐引用方式 GB/T 7714	雷买昌. Blazar高能辐射研究[D]. 北京. 中国科学院研究生院. 2015.