检索结果-南通市图书馆

Inner j.t kinematics and the viewing angle towards the γ-ray narrow-line Seyfert 1 galaxy 1H 0323＋342

Research in Astronomy and Astrophysics 2016年第11期16卷 87-98页

作者： Lars Fuhrmann Vassilis Karamanavis Stefanie Komossa Emmanouil Angelakis Thomas E Krichbaum Robert Schulz Annika Kreikenbohm Matthias Kadler Ioannis Myserlis Eduardo Ros Ioannis Nestoras j. anton zensus Max-Planck-Institut fur Radioastronomie Auf dem Htigel 69 D-53121 Bonn Germany Le-hrstuhl ftir Astronomie Universitat Wtirzburg Campus Hubland Nord Emil-Fischer-StralBe 31 D-97074 Wtirzburg Germany Dr. Karl Remeis-Sternwarte & Erlangen Centre for Astroparticle Physics Sternwartstr. 7 D-96049 Bamberg Germany Observatori Astronbmic Universitat de Valencia C/Catedraitico Jose Beltran 2 46980 Paterna Valencia Spain Departament d'Astronomia i Astroffsica Universitat de Valencia C/Dr. Moliner 50 46100 Burjassot Valencia Spain

Near-Eddington accretion rates onto low-mass black holes are thought to be a prime driver of the multi-wavelength properties of the narrow-line Seyfert 1 （NLS1） population of active galactic nuclei （AGNs）. Orientation effects have repeatedly been considered as another important factor involved, but detailed studies have been hampered by the lack of measured viewing angles towards this type of AGN. Here we present multi-epoch, 15 GHz VLBA images （MOj.VE program） of the radio-loud and Fermi/LAT- detected NLS 1 galaxy 1H 0323＋342. These are combined with single-dish, multi-frequency radio monitoring of the source＇s variability, obtained with the Effelsberg 100-m and IRAM 30-m telescopes, in the course of the F-GAMMA program. The VLBA images reveal six components with apparent speeds of 1 - 7 c, and one quasi-stationary feature. Combining the obtained apparent j.t speed （βapp） and variability Doppler factor （Dvar） estimates together with other methods, we constrain the viewing angle 0 towards 1H 0323＋342 to 0 ≤ 4°-13°. Using literature values of βapp and Dvar, we also deduce a viewing angle of 〈8°-9° towards another radio- and γ-ray-loud NLS1, namely SBS 0846＋513.

关键词： galaxies: active -- galaxies: j.ts -- galaxies: individual: 1H 0323+342 -- -) -rays: galaxies

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Radio observations of the first three-months of Fermi AGN at 4.8 GHz

引用

Research in Astronomy and Astrophysics 2012年第2期12卷 147-157页

作者： Nicola Marchili Thomas P.Krichbaum Lars Fuhrmann anton zensus Max-Plank-Institut fr Radioastronomie

Using the Urumqi 25 m radio telescope, sources from the first three months of the Fermi-large area telescope detected active galactic nuclei （AGN） catalog with a declination of 〉 0° were observed in 2009 at 4.8 GHz. The radio flux density ap- peared to correlate with the γ-ray intensity. Intra-day variability （IDV） observations were performed in March, April and May 2009 for 42 selected γ-ray bright blazars, and ~60% of them showed evidence of flux variability at 4.8 GHz during the IDV observations. The IDV detection rate was higher than that in previous flat-spectrum AGN samples. IDV appeared more often in the very long baseline interferometry-core dominant blazars, and the non-IDV blazars showed relatively ＂steeper＂ spectral in- dices than the IDV blazars. Pronounced inter-month variability was also found in two BL Lac obj.cts： j.112＋2244 and j.238＋1636.

关键词： galaxies: active - quasars: general - radio continuum: galaxies -gamma-rays: observations

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

High Brightness Temperatures in IDV Sources

引用

Chinese j.urnal of Astronomy and Astrophysics 2006年第5期6卷 530-542页

作者： Shan-j.e Qian T.P. Krichbaum A. Witzel j. A. zensus Xi-Zhen Zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 Max-Planck-Institut for Radio astronomie Auf dem Htige169 53121 Bonn Germany

High brightness temperatures are a characteristic feature of IntraDay Variability （IDV） of extragalactic radio sources. Recent studies of the polarization properties of some IDV sources （e.g., 1150＋812, PKS 0405-385 and 0716＋714） have shown that these sources harbor several compact IDV components with angular sizes of -10-30μas and very high polarizations （of up to -50%-70%）. These results indicate the possibility of the existence of uniform magnetic fields in the IDV components. We investigate the incoherent synchrotron and self- Compton radiation of an anisotropic distribution of relativistic electrons which spin around the magnetic field lines at small pitch angles. The brightness temperature limit caused by second-order Compton losses is discussed and compared to the brightness temperatures derived from energy equipartition arguments. It is found that anisotropic distributions of electrons moving in ordered magnetic fields can raise the equipartition and Compton brightness temperatures by a factor of up to -3-5. This would remove some of the difficulties in the interpretation of extremely high intrinsic brightness temperatures of 〉 1012 K （or apparent brightness temperatures of - 10^14 K with a Doppler factor of -30）.

关键词： radio continuum galaxies - Quasars individual PKS 0405-385

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Refractive Focusing of Interstellar Clouds and Intraday Polarization Angle Swings

引用

Chinese j.urnal of Astronomy and Astrophysics 2007年第2期7卷 215-223页

作者： Shan-j.e Qian T. E Krichbaum Long Gao Xi-Zhen Zhang A. Witzel j. A. zensus National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 Max-Planck-Institut fur Radioastronomie Auf dem Huge169 53121 Bonn Germany

Intraday variations of compact extragalactic radio sources in flux density and polarization are generally interpreted in terms of refractive scintillation from the continuous interstellar medium of our Galaxy. However, continuous polarization angle swings of - 180° （for example, the one observed in the QSO 0917＋624） could not be interpreted in this way. Qian et al. have shown that the polarization angle swing observed in the QSO 1150＋812 can be explained in terms of focusing-defocusing effect by an interstellar cloud, which occults two closely-placed polarized components. Here we further show that the polarization angle swing event observed in the QSO 0917＋624 can also be explained in this way. We also found evidence for the cloud eclipsing a non-polarized （core） component during a short period out- side the swing. A particular （and specific） plasma-lens model is proposed to model-fit the polarization swing event of 0917＋624. Some physical parameters related to the plasma-lens and the source components are estimated. The brightness temperatures of the two lensed components are estimated to be -1.6× 10^13 K. Thus bulk relativistic motion with a Lorentz factor less than -20 may be sufficient to avoid the inverse - Compton catastrophe.

关键词： radio continuum galaxies - polarization intraday variability - scattering refractive focusing - quasars Individual QSO 0917+624

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Periodicity of the ej.ction of superluminal components in 3C345

引用

Chinese j.urnal of Astronomy and Astrophysics 2009年第2期9卷 137-150页

作者： Shan-j.e Qian A. Witzel j. A. zensus T. R Krichbaum S. Britzen Xi-Zhen Zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 53121 Bonn Germany

The search for periodic behavior in Blazars has been an important subj.ct, which is helpful for providing significant clues to the structure and physical processes of their central energy engine. A binary black hole system has recently been suggested for causing precession of relativistic j.ts and rotation of the ej.ction position angle of VLBI knots in superluminal sources. It has been suggested that in QSO 3C345, the ej.ction direction of the superluminal knots rotates due to the precession of the central engine and thus the ej.ction position angle of the successive knots shows a periodic behavior. Some authors argue for a period of precession being ～5.6 yr （Abraham ＆ Caproni）, ～8-10 yr （Klare et al.） and ～9.5 yr （Lobanov ＆ Roland）. Applying the helical model proposed by Qian et al. and selecting appropriate parameters to fit the initial traj.ctories （within 0.3 mas） of all the components （C4 to C10）, we derive the relation between the ej.ction position angle of the components and their precession phase, and thus find a 6.9-year precession period （4.3 yr in the source frame）, which can fit the ej.ction position angle of all these superluminal knots well. Since the VLBI observations have covered more than two precession periods, confirmation in one or more future periods would be important. In addition, we emphasize that the initial parts of the traj.ctories of these knots can be fitted by a common helical pattern （channel） through a precessing of its initial phase. This scenario （or helical precessing model） is different from the usual ballistic precessing model in which the individual superluminal knots move along straight-lines after ej.ction （Tateyama ＆ Kingham）.

关键词： radio continuum galaxies -- quasars individual 3C345

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A new three-stage evolution model for millimeter to centimeter wavelength outbursts in BL Lacertae

引用

Research in Astronomy and Astrophysics 2010年第1期10卷 47-66页

作者： Shan-j.e Qian T. P. Krichbaum A. Witzel j. A. zensus Xi-Zhen Zhang H. Ungerechts H. D. Aller M. E Aller National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Max-Planck-Institut fur Radioastronomie Auf dem Hugel 69 Bonn 53121 Germany Instituto Radioastronomia Milimetrica （IRAM） Avenida Divina Pastora 7 Nficleo Central E-18012 Granada Spain Department of Astronomy University of Michigan Ann Arbor M148109-1042 USA

The multi-frequency light curves of BL Lacertae during 1997.5 - 1999.5 have been modeled by four outbursts, each having a 3-stage evolution in the （Sm, vm） plane with distinct rising-plateau-decaying phases. It is shown that the observed light curves can be well fitted for the eight frequencies from 350 GHz to 4.8 GHz. The main characteristics of the model-fitting are; （1） the outbursts are found to have very flat spectra with an optically thin spectral index α （defined as Sv α u^-α） of about 0.15. This is consistent with the results previously obtained by Valtaoj. et al. （1992）; （2） it is found that there is no spectral flattening between the rising-plateau phase and the decay phase. In other words, the optically thin spectral index does not change from the rising-plateau phase to the decay phase. These features are in contrast to the 3-stage shocked-in-j.t model proposed by Marscher ＆ Gear （1985） for submm- IR-optical flares, in which a spectral flattening of △α = 0.5 is predicted when a transition occurs from the Compton/synchrotron phase （or rising-plateau phase） to the adiabatic phase （or decay phase） with α≥ 0.5 for the shock being non-radiative. We propose a new model to interpret the fitting results, suggesting that the 3-stage evolution of the mm-cm outbursts in BL Lacertae may be related to the process of shock formation and propagation in a highly collimated j.t （for example, a ＇parabolic＇ j.t）. In particular, during the rising phase, the thickness of the synchrotron-radiating region created by the shock may rapidly increase with time （relative to the j.t width） due to the rapid inj.ction of relativistic electrons and a magnetic field, and this leads to the observed behavior that the turnover flux density Sm rapidly increases while the turnover frequency um decreases. In the decay phase, the emitting plasma enters into a free expansion regime without further inj.ction of relativistic electrons and a magnetic field （for example, when a transition from a co

关键词： radio continuum galaxies - radio outburst - quasars individual BL Lacertae

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A Possible Periodicity in the Radio Light Curves of 3C 454.3

引用

Chinese j.urnal of Astronomy and Astrophysics 2007年第3期7卷 364-374页

作者： Shan-j.e Qian N. A. Kudryavtseva S. Britzen T. E Krichbaum Long Gao A. Witzel j. A. zensus M. E Aller H. D. Aller Xi-Zhen Zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 Max-Planck-institut ftir Radioastronomie Auf dem HUgel 69 53121 Bonn Germany Astronomy Department University of Michigan Ann Arbor MI 48109 USA Astronomical Institute of St.-Petersberg State University Petrodvoretz St.-Petersburg Russia International Max-Planck Research School for Radio and Infrared Astronomy at the Universities of Bonn and Cologne

During the period 1966.5-2006.2 the 15 GHz and 8 GHz light curves of 3C 454.3 （z = 0.859） show a quasi-periodicity of ,-12.8 yr （-6.9 yr in the rest frame of the source） with a double-bump structure. This periodic behaviour is interpreted in terms of a rotating double-j.t model in which the two j.ts are created from the black holes of a binary system and rotating with the period of the orbital motion. The periodic variations in the radio fluxes of 3C 454.3 are suggested to be mainly due to the lighthouse effects （or the variation in Doppler boosting） of the precessing j.ts caused by the orbital motion. In addition, variations in the rate of mass accreting onto the black holes may be also involved.

关键词： radio continuum galaxies - Quasars individual 3C 454.3

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Refractive Focusing by Interstellar Clouds and the Rapid Polarization Angle Swing in QSO 1150+812

引用

Chinese j.urnal of Astronomy and Astrophysics 2006年第1期6卷 1-14页

作者： Shan-j.e Qian T. P. Krichbaum Xi-Zhen Zhang L. Fuhrmann G. Cimò A. Kraus T. Beckert S. Britzen A. Witzel j.A. zensus National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 53121 Bonn Germany Max-Planck-Institut für Astronomie KSnigstuhl 17 69117 Heidelberg Germany

A very rapid polarization position angle swing of -180° （with a time scale of ,-6 hours） observed at 2 cm in QSO 1150＋812 （z = 1.25） was reported by Kochenov ＆ Gabuzda. This very rare event is difficult to explain. We found a possible interpretation in the framework of a source model consisting of three polarized components, in which two compact polarized components are nearly simultaneously occulted by an interstellar cloud, with consequent focusing-defocusing effects. A specific plasma-lens model is proposed which can reasonably fit the polarized flux density curve with results derived for the two lensed components. Some physical parameters of the plasma-lens and the source components are estimated. The two compact polarized components are estimated to have brightness temperatures of -6 ×10^12 K. Thus a bulk relativistic motion with a Lorentz factor less than 10 is required to meet the inverse-Compton limit.

关键词： radio continuum: galaxies - galaxies: compact - polarization - scattering- quasars: individual: 1150+812

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Multifrequency Polarization Variations in the Quasar 0917+624

引用

Chinese j.urnal of Astronomy and Astrophysics 2002年第4期2卷 325-346页

作者： Shan－j.eQian A.Kraus 等 NationalAstronomicalObservatories ChineseAcademyofSciencesBeijing100012 Max－Planck－InstitutfuerRadioastronomie AufdemHuegel6953121BonnGermany

We present a detailed analysis of multi-frequency observations of linear polarization in the intraday variable quasar 0917+624 (z = 1.44). The observations were made in May 1989 at five frequencies (1.4, 2.7, 5.0, 8.3 and 15GHz) with the VLA and the Effelsberg 100 m-telescope and in December 1988 at two frequencies (2.7 and 5.0 GHz) with the latter. It is shown that the relationship between the variations of the polarized and total flux density is highly wavelength dependent, and the multi-frequency polarization behavior may be essential for investigating the mechanisms causing these variations. It is shown that the variations observed at 20 cm can be interpreted in terms of refractive interstellar scintillation. However, after subtracting the variation due to scintillation, three 'features' emerged in the light-curve of the polarized flux density, indicating an additional variable component. Interestingly, these features are shown to be correlated with the variations at 2-6 cm, thus indicating that these features and the associated variations are due to some intrinsic causes. Moreover, a very rapid polarization angle swing of - 180° observed in December 1988 which cannot be explained by refractive interstellar scintillation, may also be produced by an intrinsic mechanism. Accordingly, we use a shock model to explain the polarization variations observed at the higher frequencies, although scintillation could also exist. The shock model can explain not only the variation of intensity, but also the time variation of its degree and angle of polarization, including the rapid swing of the polarization angle. It is shown that the degree and angle of polarization of the shock need only vary slightly in order to account for the observed complicated behaviour of polarization.

关键词： radio continuum: galaxies - polarization - quasars: individual (QSO0917+624)

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

3C345 VLBI核心的可能的视超光速运动

引用

天文学报 1992年第4期33卷 352-361页

作者：钱善瑎 Krichbaum T.P.Witzel A. Quirrenbach A4. zensus j.A. 中国科学院北京天文台北京100080 德国Max-Planck射电天文所美国海军研究实验室美国国立射电天文台

对类星体3C345的最新VLBI观测表明,节点C_6和C_7在向西北方向作视运动,这与节点C_4在1981—1984期间的视运动大致上平行.观测到的节点C_6和节点C_7的这种视运动是与钱善瑎所提出的"核心运动模型"所作出的预测的结果相符合的.本文利用现... 详细信息

对类星体3C345的最新VLBI观测表明,节点C_6和C_7在向西北方向作视运动,这与节点C_4在1981—1984期间的视运动大致上平行.观测到的节点C_6和节点C_7的这种视运动是与钱善瑎所提出的"核心运动模型"所作出的预测的结果相符合的.本文利用现有关于3C345的所有VLBI观测数据,用比较严格的方法,定出了3C345的VLBI核心的南北方向视运动曲线和各个节点的视运动所沿的共同轨道的形式.结果表明,3C345的VLBI核心的南北方向视运动是振荡式的(见图4),导出的最大视运动速度为(0.10—0.15)mas/yr(即2c或3c,H_0=100公里·秒^(-1)·百万秒差距^(-1)).在1993年之前,对节点C_6和节点C_7的视轨道的VLBI监测,对于检验这个模型具有决定性的意义.非常希望对VLBI核心用VLBI相位参考技术来进行视运动的直接测定.

关键词： VLBI核心视超光速运动 3C345

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：