活动星系核中的软X射线超辐射起源
文献类型：学位论文
| 作者 | 钟晓谷 |
| 学位类别 | 硕士 |
| 答辩日期 | 2013-05 |
| 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 | 活动星系核 吸积盘 磁重联 X射线 |
| 其他题名 | The Origin of the Soft X-ray Excess in Active Galactic Nuclei |
| 学位专业 | 天体物理 |
| 中文摘要 | 软X射线超是活动星系核(Active Galactic Nuclei,AGN)的重要组成部分，特别是一型的活动星系核(即吸积盘轴线与视线倾角小于90度的一类活动星系核)有着明显的软X射线超现象。活动星系核的辐射可以覆盖全波段，在X射线波段，1$keV$以下，辐射流量明显大于硬X射线波段(2-10$keV$)流量。同时，幂指数快速上升，从谱型上看会形成一个突起，这便是软X射线超。但是对于软X射线超的起源一直没能得到有效的解决。此前认为软X射线超如同大蓝包一样起源于吸积盘的辐射，但是根据经典的吸积盘理论，要使得吸积盘的辐射能够达到X射线波段的辐射就必须要让中心黑洞质量很小，同时吸积盘吸积率接近爱丁顿吸积率。但实际观测表明，发现存在明显软X射线超的源并没有严格服从这些条件，因此利用经典的吸积盘模型来解释软X射线超存在困难。同时，观测表明软X射线超对应黑体谱的温度稳定，大致就在0.1-0.2$keV$附近。这个也是经典的吸积盘模型很难解释的。后继相续提出了很多模型对软X射线超进行解释，如吸收反射模型、Slim盘模型、盘风模型、热康普顿模型等。但是这些模型或多或少都会存在一些困难，并不是最佳的解释方案。对于软超的起源需要寻求其他的解决方案。磁场普遍存在于等离子体各种物理机制里面，因此我们将磁场考虑进软X射线超的起源很有必要。在吸积盘的较差转动以及湍流的作用下，磁场会不可避免的缠绕而产生磁重联。在磁重联的作用下，会产出激波，激波会使得吸积盘中的热电子加速转变成非热电子，这些非热电子会通过逆康普顿散射而冷却，同时释放出高能光子。我们考虑磁重联的能量转换很可能是软X射线超的起源。最后我们选择了25个具有明显软X射线超的源进行拟合，结果可以很好的拟合。 |
| 英文摘要 | The soft X-ray excess is a major component of many type 1 active galactic nuclei(AGN),especially Narrow Line Seyfert1 (NLS1) galaxies. The radiation of Active galactic nuclei can cover all band.Below 1 $keV$ in the X-ray band, the X-ray data are above the low energy extrapolation of the best fitting 2-10 $keV$ power law by index about $\Gamma\sim2.0$. This is so-called soft X-ray excess. However, the origin of the soft X-ray excess is unclear and difficult to explain. In some previous works that consider the black body radiation from accretion disc can emit the soft X-raylike as the "Big Blue Bump". But according to the standard accretion disc model, if the soft X-ray can be radiated from accretion disc, the mass of black hole must be small as well as the accretion rate should be close or exceed the Eddington accretion rate. However, the observation shows that the sample of AGNs with soft X-ray excess do not obey those conditions. So that it is difficult to use the standard accretion disc model to explain the origin of the soft X-ray excess. At the same time, the blackbody temperature of the soft X-ray excess remains remarkably constant at 0.1-0.2$keV$. Since then, many models are present to explain the origin of the soft X-ray excess, such as reflection and absorption model, "Slim disc", disc wind model, thermal comptonization and so on. But those models more or less have some difficult, so the origin of the soft X-ray excess is still controversial.So we can quest a new scenario to explain the Soft X-ray excess in AGNs. Because magnetic field exist in plasma generally, so it is necessary to consider magnetic field into the radiative processes of the soft X-ray. Under the effect of differential rotation of the accretion disc and turbulence, magnetic field should be tangled to generate magnetic reconnection. Then, electrons are accelerated by shock wave and turbulence triggered by magnetic reconnection, then they take place inverse Compton scattering with the soft photon which generate from accretion disc that contributes soft X-rays. We then apply the model to fit the spectra of AGNs with strong soft X-ray excess. |
| 学科主题 | 天文学 |
| 语种 | 中文 |
| 页码 | 54 |
| 源URL | [http://ir.ynao.ac.cn/handle/114a53/5098]  |
| 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 | 钟晓谷. 活动星系核中的软X射线超辐射起源[D]. 北京. 中国科学院研究生院（云南天文台）. 2013. |
入库方式： OAI收割
来源：云南天文台
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