| 摘要 | 本文详细介绍了我们关于活动星系核(Active Galactic Nuclei, AGN)吸积盘辐射以及宽发射线区的观测研究。活动星系核是剧烈活动的星系中心，从pc尺度的区域中产生等于甚至大于整个星系的辐射。 一般认为，活动星系核中心存在超大质量黑洞，物质下落的过程中，由于存在角动量，形成了吸积盘。 标准吸积盘理论认为，明亮活动星系核的吸积盘产生多温黑体谱，最高温度为10 eV左右。 其中低质量高吸积率的窄线赛弗特1型星系(Narrow Line Seyfert 1s, NLS1s)吸积盘温度能够达到40 eV，在软X射线波段形成超出。 这个理论应用广泛，迄今为止只有唯一的一个直接证据: RX J1633+4718 (Yuan et al., 2010)。 而其他大多数软X射线超的温度都在0.1 keV附近。 这种源对于吸积盘的理论研究具有重要意义，因此寻找更多这样的源是很重要的。 吸积盘的辐射照亮了外面的宽发射线区，产生宽发射线。一般将观测到宽发射线的源称为I型，没有观测到宽发射线的源称为II型。 活动星系核统一模型认为，I型和II型活动星系核本质上是相同的。 只是因为I型活动星系核的倾角小，连续谱发射区及宽发射线区没有被宽发射线区外的尘埃环遮蔽， 能够直接看到连续谱及宽发射线，所以有宽线也有光变。 而II型的倾角大，连续谱和宽发射线区被尘埃环遮蔽，所以，没有宽线，也没有光变。 但最近发现了没有被遮蔽，仍看不到宽发射线的源，就是所谓的无遮蔽II型活动星系核。 一般认为无遮蔽的II型活动星系核内禀无宽发射线。 这类源对宽线区形成的研究有重要意义。但现在只有屈指可数的几个。 本文详细介绍的我们在这两方面的工作。 第二章介绍了关于可能起源于吸积盘热辐射的软X射线超的观测研究。 由于NLS1s的吸积盘热辐射对软X射线波段贡献大，我们在NLS1s中寻找更多类似于RX J1633+4718，软超可能起源于吸积盘X射线热辐射的源。 我们处理和分析了所有已知NLS1s的ROSAT定点观测数据, 得到了软X射线超的温度, 共计150个源的245次观测。 其中58个源的90次观测具有显著的软X射线超。 大多数源的软超温度都在0.1 keV附近，只有5个源的6次观测温度小于60 eV。 这五个源中，一个是已知的RX J1633+4718，一个源的信噪比比较低。 另外三个源的软X射线超不能排除是吸积盘的X射线热辐射起源。 同时，我们证实了软超温度$T_{\rm soft}$与黑洞质量$M_{\rm BH}$，爱丁顿比$L/L_{\rm Edd}$ 以及估计的吸积盘最高温度$T_{\rm soft}$不相关，普通的软X射线超不是起源于吸积盘的X射线热辐射。 第三章介绍我们新发现的一个无遮蔽的II型活动星系核，SDSS 012032.2-005501.9。 它是我们使用stripe 82的测光数据在对SDSS DR7光谱分类为星系或未知的源进行分析的过程中发现的，没有宽发射线但具有显著光变。 我们处理和分析了SDSS 012032.2-005501.9的SDSS光谱，设定了H$\beta$宽线的等值宽度上限。90\%上限为11.8$\rm \AA$，小于所有I型活动星系核的H$\beta$等值宽度。 即，SDSS 012032.2-005501.9不存在宽发射线或者极其弱。我们还对SDSS 012032.2-005501.9的Stripe 82光变曲线进行了统计分析，并计算了g, r, i各波段的结构函数。 发现它具有在 g, r, i 波段具有显著光变，并且，光变性质与普通I型活动星系核相同。即我们直接看到了SDSS 012032.2-005501.9的连续谱发射区。它并没有被遮蔽。即，SDSS 012032.2-005501.9为一个无遮蔽的II型活动星系核。 同时，它的[OIII]光度是它的连续谱预期的[OIII]光度的20倍。 说明它可能是一个正在熄灭的活动星系核。 第四章是总结和展望。 |
| 其他摘要 | In this thesis we study the accretion disk and the broad emission lines of the Active Galactic Nuclei(AGN) with X-ray and optical observations. AGN refers to the active phenomena in the nuclei of galaxies. It is generally considered that there exists a super massive black hole (SMBH) surrounded by the accretion disk in the center of the AGN. In bright AGNs, the accretion disk is expected to be optically-thick standard accretion disk. The emission from the accretion disk is proposed to be multi-temperature blackbody radiation, with the maximum temperature around 10 keV. For objects with low black hole mass and high accretion rate, i.e., the Narrow Line Seyfert 1 galaxies (NLS1s), the maximum temperature is supposed to be 10 eV to 40 eV, which may lead to an excess in the soft X-ray band. This theory is widely accepted. However, only one source, RX J1633+4718, was found to directly suggest such a picture. It is interesting to search for more objects like RX J1633+4718, whose temperature and luminosity of the soft X-ray excess are consistent with the prediction of the standard accretion disk. The radiation from the disk photoionizes atoms or ions in the broad line region and produces broad emission lines (BELs). In general, objects with/without BELs detected are classified as type I and type II AGNs. The difference between type I and type II AGNs are generally attributed to the effect of obscuration of the dust torus. However, there are some objects without BELs found to be unobscured, which is called unobscured type II AGNs. The lack of BELs is expected to be intrinsic. The investigation of them may shed light on the formation of BEL region. Since there is only 5 such objects found up to now, it would be interesting to search for more unobscured type II AGNs. Our work on these two types of objects are presented in this thesis. In Chapter 2 we describe the work on the evidence of the thermal radiation of accretion disk in the X-ray band. Since the soft X-ray radiation from the accretion disk is relatively higher in NLS1s, we investigate the properties of the soft X-ray excess in NLS1s with ROSAT PSPC data. In total there are 245 observations for 150 NLS1s studied, with 90 observations for 58 objects showing significant soft X-ray excess. The temperature of 6 observations for 5 objects is less than 60 eV. The soft X-ray excess of three objets might originate from the thermal emission of the accretion disk. The correlation of the temperature of the soft X-ray excess and black hole mass and/or Eddington ratio are also investigated. No significant correlation is found. It is confirmed that the soft X-ray excess of most AGNs do not originate from the thermal emission from the accretion disk. In Chapter 3 we discuss a new unobscured type II AGN, SDSS 012032.2-005502. This object is a significantly variable object without BELs. It is identified in the investigation of the objects classified as galaxies in SDSS DR7 spectrum with the photometric data in the SDSS-II Supernova Survey (Stripe 82). The 90\% upper limit of the Equivalent Width (EW) of the broad component of H$\beta$ is found to be 11.8$\rm \AA$, which is less than that of any type I AGNs. The BELs in SDSS 012032.2-005502 must be absent or at least extremely weak. The analysis of the Stripe 82 data of this object shows that it varies significantly and harmoniously in g, r and i bands. The variability amplitude is higher in shorter band,e.g., the bluer, the brighter, as typical type I AGNs do. With the structure function we also found that the amplitude is higher at larger time scale. The index of the structure function is 0.28$\pm$0.06, consistent with that of typical type I AGNs. It indicates that the continuum of this object is originated from the same way of the type I AGNs. That is to say SDSS 012032.2-005502 is an unobscured type II AGN. As one of the unobscured type II AGNs, SDSS 012032.2-005502 shows no Big Blue Bump, which may result in the absent of BELs. The luminosity of [OIII] emission lines is 20 times larger than that predicted according to the continuum. A reasonable interpretation is that the continuum produced [OIII], which is emitted thousands of years before, is 20 times larger than that now. It indicates that SDSS 012032.2-005502 may be a dying AGNs. |
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