排序方式： 共有19条查询结果，搜索用时 15 毫秒
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K.. Gabnyi N. Marchili T.P. Krichbaum S. Britzen L. Fuhrmann A. Witzel J.A. Zensus P. Müller X. Liu H.G. Song J.L. Han X.H. Sun 《Astronomische Nachrichten》2007,328(8):863-866
Short time‐scale radio variations of compact extragalactic radio quasars and blazars known as IntraDay Variability (IDV) can be explained in at least some sources as a propagation effect; the variations are interpreted as scintillation of radio waves in the turbulent interstellar medium of the Milky Way. One of the most convincing observational arguments in favor of a propagation‐induced variability scenario is the observed annual modulation in the characteristic time scale of the variation due to the Earth's orbital motion. So far there are only two sources known with a well‐constrained seasonal cycle. Annual modulation has been proposed for a few other less well‐documented objects. However, for some other IDV sources source‐intrinsic structural variations which cause drastic changes in the variability time scale were also suggested. J1128+592 is a recently discovered, highly variable IDV source. Previous, densely time‐sampled flux‐density measurements with the Effelsberg 100‐m radio telescope (Germany) and the Urumqi 25‐m radio telescope (China), strongly indicate an annual modulation of the time scale. The most recent 4 observations in 2006/7, however, do not fit well to the annual modulation model proposed before. In this paper, we investigate a possible explanation of this discrepancy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Shan-jie Qian Xi-zhen Zhang S. Britzen A. Witzel T. Krichbaum A. Kraus E. Valtaoja H.D. Aller 《Chinese Astronomy and Astrophysics》1998,22(4):409-418
During the period of 1991–1993 two strong high energy γ-ray flares were observed by the Compton Gamma Ray Observatory in the flat spectrum radio source PKS 0528+134. They were associated with strong mm-radio outbursts with a few months time-delays. In this paper the spectral energy distributions (SED) of the radiations in the γ-hand X-ray and the IR-optical bands are analysed. It is shown that the high energy γ-ray radiation may be due to the inverse Compton scattering of the ambient UV and soft X-ray photons by the relativistic electrons in the jet. Basing on the comparison between the properties of the synchrotron radiation of the γ-ray source and the spectral evolution of the mm-radio outbursts, the evolutional relationship between the γ-ray emitting blobs and the mm-radio emitting blobs is discussed. 相似文献
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Shan-Jie 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 《中国天文和天体物理学报》2007,7(3):364-374
During the period 1966.5–2006.2 the 15GHz and 8GHz 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-jet model in which the two jets 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 jets caused by the orbital motion. In addition, variations in the rate of mass accreting onto the black holes may be also involved. 相似文献
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Shan-Jie Qian A. Kraus Xi-Zhen Zhang T. P. Krichbaum A. Witzel J. A. Zensus National Astronomical Observatories Chinese Academy of Sciences Beijing Max-Planck-Institut fur Radioastronomie Auf dem Hugel Bonn Germany 《中国天文和天体物理学报》2002,2(4):325-346
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 thes 相似文献
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The brightness temperature of 433 Eros was less than 460°K during the close opposition in January 1975. 相似文献
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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 (S m,νm) plane with distinct rising–plateau–decaying phases.It is shown that the observed light curves can be well fitted for the eight frequencies from 350GHz to 4.8GHz.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 Sν∝ν-α) of about 0.15.This is consisten... 相似文献
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We have investigated the fine structure of the object 1803+784 at a wavelength of 18 cm with an angular resolution of ～0.5 mas. The structure consists of a core (injector) and a jet. The angle of the relativistic plasma outflow is equal to the angle of a conical diverging helix—the trajectory of compact components, suggesting a similar shape of the jet. The helical structure and the curvature of the jet axis are assumed to be determined by rapid and long-period precession of the rotation axis. The core radio emission at 18 cm is attenuated by absorption in the ambient ionized medium (cocoon wall) by >25 db. The bright compact component is the nearby part of the jet extending outside the dense part of the screen. Ionization variations in the medium cause low-frequency radio variability. Screen parameters are estimated. 相似文献
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Intraday variations of compact extragalactic radio sources in flux density and po- larization 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 ～1.6×1013 K. Thus bulk relativistic motion with a Lorentz factor less than ～20 may be sufficient to avoid the inverse - Compton catastrophe. 相似文献