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1.
本给出了ＲＯＳＡＴ ＰＳＰＣ对ＮＧＣ５４８定点观测的分析结果，在ＲＯＳＡＴ观测期间，ＮＧＣ５５４８的计数率显示出大振幅的变化，变化高达１４倍，硬度比与计数率呈负相关，这是由于ＮＣＧ５５４的软Ｘ射线辐射除幂律分量外还有一个“软超”分量，分别用黑体辐射和热韧致辐射来拟合这个“软超”辐射，得出“软超”的热温度分别为：黑体辐射模型是０．０８ｋｅＶ，热韧致辐射模型是０．２３ｋｅＶ。 相似文献
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赵永恒 《中国天文和天体物理学报》1997,(4)
本文给出了ＲＯＳＡＴＰＳＰＣ对ＮＧＣ５５４８定点观测的分析结果．在ＲＯＳＡＴ观测期间，ＮＧＣ５５４８的计数率显示出大振幅的变化，变化高达１４倍．硬度比与计数率呈负相关，这是由于ＮＧＣ５５４８的软Ｘ射线辐射除幂律分量外还有一个“软超”分量，分别用黑体辐射和热韧致辐射来拟合这个“软超”辐射，得出“软超”的热温度分别为：黑体辐射模型是０．０８ｋｅＶ，热韧致辐射模型是０．２３ｋｅＶ． 相似文献
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从射电结构的角度评述了ＢＬＬａｃ天体和ＦＲ－Ｉ射电星系的统一模型的最新进展，内容包括射电结构，延展射电光度（Ｐｅｘｔ），最大角尺度（ＬＡＳ），射电核主导系数（ｆ）的比较以及对相对论聚束的测试。最新的射电观测资料表明ＸＢＬｓ是介于ＦＲ－Ｉ和ＲＢＬｓ之间的过渡型天体，这对ＢＬＬａｃ天体是聚束的ＦＲ－Ｉ射电星系提供了一个很好的证据。 相似文献
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我们发现利用ＷｏｌｆＲａｙｅｔ 星系的远红外射电相关关系可以对ＬＩＮＥＲ 的激发机制初步分类。非常有意思的一个现象是几乎所有有内环结构的ＬＩＮＥＲ 都是星暴占主导的源,它们的ＡＧＮ 活动比ＡＧＮ 占主导的ＬＩＮＥＲ 要低。我们还发现对年龄大于１０７ 年的星暴星系或复合类天体（ＡＧＮ 和星暴的贡献相当的天体） 来说,激波加热尘埃的机制可能是很重要的。 相似文献
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使用澳大利亚致密阵（ＡＴＣＡ）在１．４ＧＨｚ上观测一个极 度的ＩＲＡＳ星系样本。在这个样本所包括的３７个ＩＲＡＳ星系中,探测到１９个源的射 电发射 ,获得了它们的射电参数,如峰值位置,射电流量等。该样本的射电功率范围在２２．９〈ｌｏｇＰ１．４Ｇ（Ｗ／Ｈｚ）〈２３．８,本文给出了观测的初步结果。 相似文献
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研究表明活动星系核的高能γ射线辐射和低频射电辐射有着某些内在的联系。ＥＧＲＥＴ已检测到６６ 颗可信度很高的活动星系核。而这些高能的活动星系核有部分缺少足够的射电图象观测。为研究这些河外剧变源的射电辐射性质及致密结构,并研究活动量系核射电喷流弯曲与高能辐射的内在联系。我们利用国际欧洲ＶＬＢＩ网,英国的ＭＥＲＬＩＮ 和美国的ＶＬＡ对近２０ 颗γ射线活动星系核进行了观测。本文给出部分高能γ射线活动星系核在８ ．５ＧＨｚ的ＶＬＡ 观测图象。 相似文献
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ＲＯＳＡＴ卫星的全天巡天观测到了一大批射电星系和各种活动星核,为我们研究这些活动性剧烈的河外天体的辐射机制、多波段辐射相关性以及各类星系核之间的演化联系提供了重要数据。通过将ＲＯＳＡＴ全天巡天观测与ＰＭＮ射电（５ＧＨｚ）巡天观测进行交叉证认,我们得到了６４２颗天射电源。对这些对应体随后进行的光学证认构建了一个星系和活动星系核的大样本。其中３１１个对应体（占５２％）被过去的光学观测证实为河外天体（包 相似文献
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棒旋星系ＮＧＣ７５８２的光学发射线显示出它具有Ｓｅｙｆｅｒｔ２和星爆星系的双重特点。本利用射电和红外观测数据对它中心区附近的性质进行了研究。结果表明ＮＧＣ７５８２中心附近可能存在着一个活动性很强的恒星形成区,恒星的形成率比银河系高得多,星爆对这个Ｓｅｙｆｅｒｔ２星系的性质起了重要作用。 相似文献
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塞佛特星系ＮＧＣ1 0 6 8是一个非常令人注目的特殊天体 ,它是Ｓｅｙｆｅｒｔ[1]发现的第一批此类星系中离我们最近 (1 9Ｍｐｃ,取Ｈ0 =6 0ｋｍｓ- 1Ｍｐｃ- 1)和最亮的一个塞佛特星系 ,因此天文学家从射电到Ｘ 射线整个电磁波段对它进行了详尽的观测和研究。ＮＧＣ1 0 6 8最初被归类为塞佛特ＩＩ型天体 ,但是通过对其偏振光的光谱观测 ,发现了认为被遮挡住的塞佛特Ｉ型核发出的± 432 0ｋｍ/ｓ的宽Ｈβ发射线 ,因此被认为是活动星系核统一模型的一个范例 (见文 [2 ] )。射电与光学的观测资料都表明ＮＧＣ1 0 6 8的中心部分有激烈的喷射活动… 相似文献
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ＡＧＮ天体的主要特征之一，就是它们的光谱中有宽而强的发射线，因此，这些宽发射线的产生区域ＢＬＲ为人们提供了一个了解ＡＧＮ天体物理本质的独特而重要的场。在文中围绕讨论了ＢＬＲ基本物理特征，评述近年来有关的理论和观测研究进展及其现状在文（Ⅱ）中主要涉及ＢＬＲ的几何结构和尺度及其运动学研究的进展和现状。 相似文献
11.
光学波段的“变脸”AGN (changing-look Active Galactic Nucleus, CL AGN)是光谱类型发生变化AGN的统称.近年来,越来越多观测证据表明这类现象与中央超大质量黑洞吸积活动有关.而黑洞吸积率的变化可能会引起喷流的增强或者减弱,进而导致射电波段观测性质的变化.在已发表的文献中,收集了74个光学波段证认的“变脸”AGN、90个“变脸”AGN的候选体.基于这个目前最大并且选源方式多样化的非完备样本,探讨了“变脸”AGN在射电波段的观测性质.从澳大利亚平方公里阵先导设备(Australian Square Kilometre Array (SKA) Pathfinder, ASKAP)和美国甚大阵甚大阵(Very Large Array, VLA)的4大射电巡天观测中,发现了51个“变脸”AGN (含21个候选体)在0.9–3 GHz存在射电波段的对应体,样本的射电探测率约为41%,与一般AGN的射电探测率无显著区别.此外,分析了这些源的射电谱指数,发现在1.4 GHz和3 GHz频段“变脸”AGN相对于一般射电源有较平的射电谱.该统计结果或可解释为“... 相似文献
12.
《Chinese Astronomy and Astrophysics》2023,47(2):285-308
Optically “changing-look” active galactic nuclei (AGNs) are a class of objects that exhibit appearance or disappearance of broad lines. Recent studies have shown that these “changing-look” activities very likely result from the accretion activities of the central supermassive black holes. Large variation of the accretion rate might cause jet ejection and fading events, thus lead to a certain variability of observational radio properties. From the published literature, 74 “changing-look” AGNs and 90 “changing-look” AGNs candidates identified in optical observations were collected. Based on this largest, complex, and incomplete sample to date, the radio properties of “changing-look” AGNs were investigated. The radio counterparts of 51 “changing-look” AGNs (including 21 candidates) were discovered from the all-sky surveys conducted by the Australian Square Kilometre Array Pathfinder (ASKAP) and Very Large Array (VLA) covering the frequency range of 0.9–3 GHz. This corresponds to a detection rate of about 41 percent, which is similar to general AGNs. The radio spectral indices between 0.9 and 1.4 GHz and between 1.4 and 3 GHz were calculated, which suggest that these “changing-look” AGNs tend to have flatter radio spectra than normal AGNs. This statistical result indicates that “changing-look” AGNs might host some young, compact, and faint radio jets. 相似文献
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Summary. Recent papers dealing with the most controversial aspects of AGNs are reviewed. They suggest interesting conclusions: all
Seyferts can be described by a single parameter, the X-ray column density; radio loud AGNs may host a rapidly spinning black
hole and radio quiet AGNs a slowly spinning black hole; high-ionization AGNs (Seyfert galaxies and QSOs) contain an optically
thick, geometrically thin accretion disk, while low-ionization AGNs (Liners) contain an optically thin, geometrically thick
accretion disk; a number of blazars have been classified as BLLs on the basis of insufficient data; most objects with weak
broad emission lines are in fact HPQs; many objects have been called Liners although they are not AGNs but rather the result
of stellar activity; type 2 QSOs exist, but are quite inconspicuous if radio quiet.
Received 16 November 1999 / Published online: 15 February 2000 相似文献
14.
We propose an explanation of the origin of the central radio gaps which are usually observed in extragalactic radio sources that exhibit jet structures.An estimate was made of neutron Lorentz factors of neutrons responsible for energy transport from the central engine of active galactic nuclei (AGNs) to the jet turn-on point of typical AGNs.The probable explanations of the existence of different belts in the radio gap morphology was attempted. 相似文献
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Jun-Hui Fan Jiang-He Yang Jing Pan Tong-Xu Hua Center for Astrophysics Guangzhou University Guangzhou China Astronomy Science Technology Research Laboratory of 《中国天文和天体物理学报》2011,(12)
Active galactic nuclei(AGNs)have two major classes,namely radio loud AGNs and radio quiet AGNs.A small subset of the radio-loud AGNs is called blazars,which display extreme observational properties,such as rapid variability,high luminosity,high and variable polarization,and superluminal motion.All of those observational properties are probably due to a relativistic beaming effect with the jet pointing close to the line of sight.Observations suggest that the orientation can be expressed by a core-dominance p... 相似文献
18.
A. Caccianiga M.J.M. Marchã A. Thean J. Dennett-Thorpe 《Monthly notices of the Royal Astronomical Society》2001,328(3):867-872
We present and discuss the results of very-long baseline interferometry (VLBI, EVN) observations of three low-luminosity broad emission line active galactic nuclei (AGNs) carefully selected from a sample of flat-spectrum radio sources (CLASS). Based on the total and the extended radio power at 5 and at 1.4 GHz respectively, these objects should be technically classified as radio-quiet AGN and thus the origin of their radio emission is not clearly understood. The VLBI observations presented in this paper have revealed compact radio cores which imply a lower limit on the brightness temperature of about . This result rules out a thermal origin for the radio emission and strongly suggests an emission mechanism similar to that observed in more powerful radio-loud AGNs. Since, by definition, the three objects show a flat (or inverted) radio spectrum between 1.4 and 8.4 GHz, the observed radio emission could be relativistically beamed. Multi-epoch VLBI observations can confirm this possibility in two years' time. 相似文献
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Active galactic nuclei (AGNs) form two distinct sequences on the radio-loudness–Eddington ratio plane. The ‘upper’ sequence contains radio selected AGNs, the ‘lower’ sequence is composed mainly of optically selected AGNs. The sequences mark the upper bounds for the radio-loudness of two distinct populations of AGNs, hosted, respectively, by elliptical and disk galaxies. Both sequences show the same dependence of the radio-loudness on the Eddington ratio (an increase with decreasing Eddington ratio), which suggests that another parameter in addition to the accretion rate must play a role in determining the efficiency of jet production in AGNs. We speculate that this additional parameter is the spin of the black hole, assuming that black holes in giant elliptical galaxies have (on average) much larger spins than black holes in disc galaxies. Possible evolutionary scenarios leading to such a spin dichotomy are discussed. The galaxy-morphology related radio dichotomy breaks down at high accretion rates where the dominant fraction of luminous quasars being hosted by giant ellipticals is radio-quiet. This indicates that the production of powerful jets at high accretion rates is in most cases suppressed and, in analogy to X-ray binary systems (XRB) during high and very high states, may be intermittent. Such intermittency can be caused by switches between two different accretion modes, assuming that only during one of them an outflow from the central engine is sufficiently collimated to form a relativistic jet. 相似文献