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1.
视超光速源的统计分析 总被引：2，自引：0，他引：2
本文收集了视超光速源样本的有关观测数据，在同步加速自康普顿散射机制下导出了各源的多普勒因子，再利用视超光速源的相对论射束模型计算样本源的有关物理量，如射电光度和亮温度，并与它们的观测值作直接的比较，得到较好的相关结果。这些结果支持了活动星系核中具有相对论射束运动的假设。同时我们比较了样本源的射电、光学、Ｘ射线的发现它们之间有一定的相关性，说明在不同波段上的辐射机制可能存在某种联系。 相似文献
2.
高频VLBI观测揭示出河外射电源在pc或者亚pc尺度上大都有核-喷流的内部结构。尤其是对平谱致密射电源中毫角秒尺度的子源，能以相当高的概率观测到它的视超光速现象。多频观测可监测到一些新喷流子源的出现，特别在射电激变源中这些新喷流子源的出现与宽带内(从光学到γ射线)的爆发相关。且得到的一些源的核区谱指数分布，为确认源的VLBI核提供了支持。 相似文献
3.
高频VLBI观测揭示出河外射电源在pc或者亚pc尺度上大都有核-喷流的内部结构，尤其是对平谱致密射电源中毫角秒尺度的子源，能以相当高的概率观测到它的视超光速现象。多频观测可监测到一些新喷流子源的出现，特别在射电激变源中这些新喷流子源的出现与宽带内（从光学到γ射线）的爆发相关。且得到的一些源的核区谱指数分布，为确认源的VLBI核提供了支持。 相似文献
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5.
在早期的文章中，基于耀变体（Blazar)的知识，我们预言了在射电噪活动星系核（AGN）中心10kpc范围内X射线喷流的存在。钱得拉（Chandra)卫星最近对低功率射电星系的X射线观测与我们的预言相一致。在本文中我们研究了kpc尺度喷流中的电子加速，并建议通过对强的FRⅡ射电星系中所预言的X射线喷流的钱得拉卫星的X射线的观测，来研究红的耀变体中的康普顿冷却以及在内部致密喷流和大尺度延伸喷流间环境的不同。以上的研究可以进一步检验我们的关于射电噪活动星系核中kpc尺度X射线喷流的模型。 相似文献
6.
作为上一篇文章的继续,本文从总结迄今已探测到的视超光速源的一般特征出发,简要地讨论了视超光速源在活动星系核分类研究中的地位;并综述了较普遍接受的对于视超光速源的一些理论探讨。文章的最后简述了目前对视超光速源观测的问题和前景。 相似文献
7.
本文提出，原则上所有活动星系核都能产生喷流，但是星系核心区域介质的渗入可能使得一部分喷流被减速以至于消失。这为喷流只见于一部分活动星系的事实提供了一种可能解释，也可能是建立活动星系核结构统一的模型的一个有意义的步骤。 相似文献
8.
水超脉泽辐射( 各向同性光度超过 10 个太阳光度) 通常在星系中心最内部的核区( 小于几个秒差距) 被发现,因而活动星系核被认为是其唯一的能量源。同其它没有检测到水脉泽辐射的活动星系核相比,水脉泽寄主活动星系核可能隐含着某种或某些特殊性质。基于此我们调研了已经公开发表的所有水脉泽源的 X 射线观测情况,得到了一个有 X 射线观测研究结果的子样本( 39 个源) 。由它们的 X 射线光度以及估算的黑洞质量,导出了它们的无量纲吸积率( logL2-10keV /LEdd,其中 L2-10keV和 LEdd分别是 2 - 10keV 的固有光度和爱丁顿光度) ; 与距离范围相当的、没有检测到水脉泽的活动星系核样本相比,发现脉泽寄主活动星系核有较高的吸积率。进一步分析比较这两个活动星系核样本的质量吸积率,也发现类似的趋势。此外,为了探索吸积率和水脉泽辐射间可能的内在联系,我们对它们的脉泽光度和吸积率进行了统计分析,然而结果显示二者之间没有明显的相关性。 相似文献
9.
对活动星系核中的喷流加速机制、观测特征有目前研究近况进行了评述。磁场在喷流加速过程中起重要作用，对磁场加速喷流模型中喷流加速区域的大小进行了估计。比较了不同的磁场加速喷流模型，并讨论了有序吸积盘磁场的形成与维持过程。简要地评述了活动星系核中吸积盘与喷流存在内在联系的观测证据，及中央黑洞与活动星系核的射电辐射特征的关系。 相似文献
10.
在源的质心固定的视超光速模型的基础上，进一步出在质心运动情况下的视超光速运动的视速度议程，在喷流方向与源的退行方面相反的情况下，推导核与子源速率相等及核固定条件下子源真实速度的方程，然后代入视速度和由自康顿效应推算的喷流与视线的夹角数据，从而求出上述极值条件下子源的真实速度，再与对应源的哈勃红移速度相对照，结果发现，源的运动对其子源的速度没有影响。 相似文献
11.
J. Fritz † A. Franceschini E. Hatziminaoglou 《Monthly notices of the Royal Astronomical Society》2006,366(3):767-786
We describe improved modelling of the emission by dust in a toroidal-like structure heated by a central illuminating source within active galactic nuclei (AGNs). We have chosen a simple but realistic torus geometry, a flared disc, and a dust grain distribution function including a full range of grain sizes. The optical depth within the torus is computed in detail taking into account the different sublimation temperatures of the silicate and graphite grains, which solves previously reported inconsistencies in the silicate emission feature in type 1 AGNs. We exploit this model to study the spectral energy distributions (SEDs) of 58 extragalactic (both type 1 and type 2) sources using archival optical and infrared data. We find that both AGN and starburst contributions are often required to reproduce the observed SEDs, although in a few cases they are very well fitted by a pure AGN component. The AGN contribution to the far-infrared luminosity is found to be higher in type 1 sources, with all the type 2 requiring a substantial contribution from a circumnuclear starburst. Our results appear in agreement with the AGN unified scheme, because the distributions of key parameters of the torus models turn out to be compatible for type 1 and type 2 AGNs. Further support to the unification concept comes from comparison with medium-resolution infrared spectra of type 1 AGNs by the Spitzer observatory, showing evidence for a moderate silicate emission around 10 μm, which our code reproduces. From our analysis we infer accretion flows in the inner nucleus of local AGNs characterized by high equatorial optical depths ( AV ≃ 100) , moderate sizes ( R max < 100 pc) and very high covering factors ( f ≃ 80 per cent) on average. 相似文献
12.
Ming Zhou Xin-Wu Cao 《中国天文和天体物理学报》2009,9(3)
We explore the relationship between black hole mass (MBH) and the motion of the jet components for a sample of blazars. The Very Long Baseline Array (VLBA) 2cm Survey and its continuation: Monitoring of Jets in active galactic nuclei (AGNs) with VLBA Experiments (MOJAVE) have observed 278 radio-loud AGNs, of which 146 blazars have reliable measurements of their apparent velocities of the jet components. We calculate the minimal Lorentz factors for these sources from their measured apparent velocities, and their black hole masses ate estimated with their broad-line widths. A sig-nificant intrinsic correlation is found between black hole masses and the minimal Lorentz factors of the jet components. The Eddington ratio is only weakly correlated with the min-imal Lorentz factor, which may imply that the Blandford-Znajek (BZ) mechanism may dominate over the Blandford-Payne (BP) mechanism for the jet acceleration (at least) in blazars. 相似文献
13.
Min-Zhi Kong Xue-Bing Wu Ran Wang Jin-Lin Han National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Astronomy Peking University Beijing 《中国天文和天体物理学报》2006,6(4):396-410
Based on measured broad line region sizes in the reverberation-mapping AGN sample, two new empirical relations are introduced to estimate the central black hole masses of radio-loud high-redshift (z > 0.5) AGNs. First, using the archival IUE/HST spectroscopy data at UV band for the reverberation-mapping objects, we obtained two new empirical relations between the BLR size and Mg II/C IV emission line luminosity. Secondly, using the newly determined black hole masses of the reverberation-mapping sample as calibration, we found two new relationships for determining the black hole mass with the full width at half maximum and the luminosity of Mg II/C IV line. We then apply the relations to estimate the black hole masses of the AGNs in the Large Bright Quasar Survey and a sample of radio-loud quasars. For the objects with small radio-loudness, the black hole mass estimated using the RBLR-LMgII/C IV relation is consistent with that from the RBLR-L3000 (?)/1350(?) relation. For radio-loud AGNs, however, the mass estimated from the RBLR-LMgII/CIV relation is sys- tematically lower than that from the continuum luminosity L3000(?)/1350(?). Because jets could have significant contributions to the UV/optical continuum luminosity of radio-loud AGNs, we emphasize once again that for radio-loud AGNs, the emission line luminosity may be a better tracer of the ionizing luminosity than the continuum luminosity, so that the relations between the BLR size and UV emission line luminosities should be used to estimate the black hole masses of high redshift radio-loud AGNs. 相似文献
14.
Minfeng Gu Xinwu Cao D. R. Jiang 《Monthly notices of the Royal Astronomical Society》2009,396(2):984-996
Based on the Königl's inhomogeneous jet model, we estimate the jet parameters, such as bulk Lorentz factor Γ, viewing angle θ and electron number density n e from radio very long-baseline interferometry and X-ray data for a sample of active galactic nuclei (AGNs) assuming that the X-rays are from the jet rather than the intracluster gas. The bulk kinetic power of jets is then calculated using the derived jet parameters. We find a strong correlation between the total luminosity of broad emission lines and the bulk kinetic power of the jets. This result supports the scenario that the accretion process is tightly linked with the radio jets, though how the disc and jet are coupled is not revealed by present correlation analysis. Moreover, we find a significant correlation between the bulk kinetic power and radio extended luminosity. This implies that the emission from the radio lobes is closely related with the energy flux transported through jets from the central part of AGNs. 相似文献
15.
Superluminal Motion and Polarization in Blazars 总被引：3，自引：0，他引：3
Jun-Hui Fan Yong-Jiu Wang Jiang-He Yang Cheng-Yue Su Center for Astrophysics Guangzhou University Guangzhou Physics Institute Hunan Normal University Changsha Department of Electronics Physics Hunan University of Arts Science Chaugde Department of Physics Guangdong Industry University Guangzhou 《中国天文和天体物理学报》2004,4(6):533-540
A relativistic beaming model has been successfully used to explain the observed properties of active galactic nuclei (AGNs). In this model there are two emission components, a boosted one and an unbeamed one, shown up in the radio band as the core and lobe components. The luminosity ratio of the core to the lobe is denned as the core-dominance parameter (R = LCore/LLobe). The de-beamed radio luminosity (Ldbjet) in the jet is assumed to be proportional to the unbeamedluminosity (Lub) in the co-moving frame, i.e., f = Ldbjet/Lub, and f is determined in ourprevious paper. We further discuss the relationship between BL Lacertae objects (BLs) and flat spectrum radio quasars (FSRQs), which are subclasses of blazars with different degrees of polarization, using the calculated values of the ratio f for a sample of superluminal blazars. We found 1) that the BLs show smaller averaged Doppler factors and Lorentz factors, larger viewing angles and higher core-dominance parameters than do the FSRQs, and 2) that in th 相似文献
16.
Active galactic nuclei (AGNs) in low surface brightness galaxies (LSBGs) have received little attention in previous studies. We present a detailed spectral analysis of 194 LSBGs from the Impey et al. (1996) APM LSBG sample which has been observed spec-troscopically by the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). Our elaborate spectral analysis enables us to carry out, for the first time, reliable spectral classification of nuclear processes in LSBGs based on the standard emission line diagnostic diagrams in a rigorous way. Star-forming galaxies are common, as found in about 52% of LSBGs. We find that, contrary to some previous claims, the fraction of galaxies that contain AGNs is significantly lower than that found in nearby normal galaxies of high surface brightness. This is qualitatively in line with the finding of Impey et al. This result holds true even within each morphological type from Sa to Sc. LSBGs that have larger central stellar ve-locity dispersions or larger physical sizes tend to have a higher chance of harboring an AGN. For three AGNs with broad emission lines, the black hole masses estimated from the emission lines are broadly consistent with the well known M-σ* relation established for normal galaxies and AGNs. 相似文献
17.
The orientations of the accretion disk of active galactic nuclei (AGN) and the stellar disk of its host galaxy are both determined by the angular momentum of their forming gas, but on very different physical environments and spatial scales. Here we show the evidence that the orientation of the stellar disk is correlated with the accretion disk by comparing the inclinations of the stellar disks of a large sample of Type 2 AGNs selected from Sloan Digital Sky Survey (SDSS, York et al. 2000) to a control galaxy sample. Given that the Type 2 AGN fraction is in the range of 70–90 percent for low luminosity AGNs as a priori, we find that the mean tilt between the accretion disk and stellar disk is ~ 30 degrees (Shen et al. 2010). 相似文献
18.
Mei-fang Zhao Chao Wu A-li Luo Fu-chao Wu Yong-heng Zhao 《Chinese Astronomy and Astrophysics》2007,31(4):352-362
By means of a batch of low-redshift spectral data of AGNs taken from the SDSS, an automated K-nearest neighbor method is developed to classify AGNs into two types: broad-line and narrow-line AGNs. According to the different characteristics of emission lines of broad-line and narrow-line AGNs, the spectral wavebands containing the Hβ, [OIII], H and [NII] emission lines are used separately or in combination in the classification. experiment. The results show that the best results are obtained when only the wavebands of H and [NII] are used, and that for a training set of size 1000 and a testing set of 3313, we can achieve a speed of 32.89 single classifications per second. It is demonstrated that, where the typical spectral features are sufficiently exploited, the automated classification method is feasible for the spectra of AGNs in largescale spectral surveys and provides a fast and straightforward alternative to classification schemes based on using the FWHM values of emission lines or the line strength ratio diagnostic diagrams. 相似文献
19.
Anne Lähteenmäki Merja Tornikoski Talvikki Hovatta Esko Valtaoja 《Astrophysics and Space Science》2007,311(1-3):347-351
A wealth of information on the properties of jets in Active Galactic Nuclei (AGNs) can be derived from total flux density observations at high radio frequencies. This includes, for example, the Doppler factor, the Lorentz factor, and the viewing angle of the jet. We have earlier calculated these parameters for a sample of ～80 sources of different AGN types using almost 20 years of 22 and 37 GHz data from Metsähovi Radio Observatory. We have now gathered data for an additional ten years, and studied the long term characteristic variability time scales of a large sample of AGNs using the first order structure function, the discrete autocorrelation function and the Lomb-Scargle periodogram. Some of the results will be presented in this paper. We also stress the importance of long term observations of AGNs, the main reason for this being misinterpretations of source properties due to insufficient time coverage. Only a few observing epochs will too easily lead to incorrect conclusions about variability, continuum spectra, and the general detectability of the source, not to mention the exclusion of interesting objects from further studies. This is particularly important when considering, for example, the Planck satellite for which the quality of the main mission product, the accurate cosmic microwave background anisotropy maps, depends heavily on the elimination of foreground sources such as AGNs. 相似文献
20.
Rosalba Perna Charles R. Keeton 《Monthly notices of the Royal Astronomical Society》2009,397(2):1084-1092
In strong gravitational lensing, the multiple images we see correspond to light rays that leave the source in slightly different directions. If the source emission is anisotropic, the images may differ from conventional lensing predictions (which assume isotropy). To identify scales on which source anisotropy may be important, we study the angle δ between the light rays emerging from the source, for different lensing configurations. If the lens has a power-law profile M ∝ R γ , the angle δ initially increases with lens redshift and then either diverges (for a steep profile γ < 1 ), remains constant (for an isothermal profile γ= 1 ), or vanishes (for a shallow profile γ > 1 ) as z l → z s . The scaling with lens mass is roughly δ∝ M 1/(2−γ) . The results for an Navarro–Frenk–White (NFW) profile are qualitatively similar to those for a shallow power law, with δ peaking at about half the redshift of the source (not half the distance). In practice, beaming could modify the statistics of beamed sources lensed by massive clusters: for an opening angle θjet , there is a probability as high as P ∼ 0.02–0.07(θjet /0.5°)−1 that one of the lensed images may be missed (for 2 ≲ z s ≲ 6 ). Differential absorption within active galactic nuclei (AGNs) could modify the flux ratios of AGNs lensed by clusters; a sample of AGNs lensed by clusters could provide further constraints on the sizes of absorbing regions. Source anisotropy is not likely to be a significant effect in galaxy-scale strong lensing. 相似文献