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1.
10颗近赤道弱源MK2 VLBI观测结果 总被引：2，自引：0，他引：2
本文给出利用中国、意大利、南非射电望远镜对一个近赤道源本在５ＧＨｚ频率上进行ＭＫ２ ＶＬＢＩ普测中１０颗弱源的相关流量和其中部分源用ＨａｒｔＲＡＯ望远镜观测的总流量值，作为进一步的ＭＫ３或ＶＬＢＡ记录系统的ＶＬＢＩ观测依据。 相似文献
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本文报道南天区５ＧＨｚＶＬＢＩ的第二轮观测．第二轮观测是在１９９３年５月期间进行的，共观测了２５个射电源，检测到２４个源，获得了２３个南天区耀变体（Ｂｌａｚａｒ）的ＶＬＢＩ高分辨率的图象，其中１５个是第一次ＶＬＢＩ成图，７个是高能（＞１００ＭｅＶ）γ射电源，１２个源呈现核－喷流结构，其余１１个源是单一的致密核，未发现致密双源．有两个源可能有视超光速现象． 相似文献
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在本文中较全面地述了天体脉泽源的ＶＬＢＩ观测方法，简单地提及ＶＬＢＩ观测研究的新进展，着重述评空间ＶＬＢＩ用脉泽的观测，并提及了地面ＶＬＢＩ的一些预备观测情况。 相似文献
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空间VLBI研究的现状和未来 总被引：4，自引：0，他引：4
空间ＶＬＢＩ卫星ＶＳＯＰ／ＨＡＬＣＡ是日本宇航科学研究所（ＩＳＡＳ）的飞行任务,已经在１９９７年２月升空。它拥有８ｍ直径的射电望远镜,远地点达２２０００ｋｍ。和地面的射电望远镜联合观测（干涉观测）,其最高分辨率比地面ＶＬＢＩ提高了３倍。该项空间ＶＬＢＩ观测由ＮＳＡＳ的地面跟踪站支持。第一批ＶＬＢＩ图像已经在因特网上发表。ＲａｄｉｏＡｓｔｒｏｎ项目由俄罗斯科学院列别捷夫物理研究所天文空间中心（ＡＳＣ 相似文献
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南天区耀变体的VLBI研究 总被引：2，自引：2，他引：0
本报道南天区５ＧＨｚＶＬＢＩ的第二轮观测，第二轮观测是在１９９３年５月期间进行的，共观测２５个射电源，检测到２４个源，获得了２３个南天区耀变体的ＶＬＢＩ高分辨率的图象，其中１５个是第一次ＶＬＢＩ成图，７个高能γ射电源，１２个泊呈现核－喷流结构，其余１１个源是单一的致密核，未发现致密双源。有两个源可能有视超光速现象。 相似文献
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使用ＢＩＭＡ的Ｃ位形混合波导联结９元天线阵,对ＳｇｒＢ２（Ｎ）和ＳｇｒＢ２（Ｍ）观测了ＣＨ３ＣＮ分子振动激发态Ｖ８＝１的６Ｋ－５Ｋ线系,仅在ＳｇｒＢ２（Ｎ）的１０″＊４″区域里探测到上述发射线。 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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ＶＬＢＩ天体物理学的发展（续）万同山（接上期）下一代的ＶＬＢＩ以ＶＬＢＡ和Ｒａｄｉｏａｓｔｒｏｎ空间ＶＬＢＩ站为代表。美国国立射电天文台的ＶＬＢＡ是世界上第一个ＶＬＢＩ专用设备，在美国领土上从夏威夷到维尔京群岛上放置了１０个２５米口径的射电望远镜，最... 相似文献
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通过主要在短厘米波长的全球ＶＬＢＩ观测，已经现强射电类星体４Ｃ３９．２５在十秒差距尺度结构中的视超光速运动，其运动学图景表明该源是一个很特殊的视超光速源，近几年已提出了若干模型，试图解释这特殊的运动图景，报道不多的百秒差距尺度的ＶＬＢＩ观测，很可能有助于检验提出的模型，本文介绍用欧洲网及上海２５ｍ天线，在１８ｃｍ波长对４Ｃ３９．２５所作的ＶＬＢＩ成象观测的初步结果，显示秒差距尺度复杂结构及可能存在 相似文献
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《New Astronomy Reviews》1999,43(8-10):629-632
We present preliminary results from a VLBI survey at λ=6 cm of a sample of 35 sources with flux densities of 2–100 mJy. These sources were selected from the VLA FIRST survey at λ=20 cm, in a 3 degree field around the bright calibrator 1156+295, simply by imposing S20>10 mJy and θ<5 arcsec. MERLIN observations at λ6 cm detected 70/127 of these sources with a threshold of 2 mJy at 50 mas resolution and the closest 35 of these to the calibrator were observed with the VLBA+EVN in snapshot mode at λ6 cm. These sources are a mixture of flat and steep-spectrum sources and include: weak flat-spectrum nuclei of large radio galaxies, low power AGN in nearby galaxies and radio quiet quasars. With these short observations, the sensitivity is limited and most appear as either core-jets or simple point sources on the milliarcsec scale. Nonetheless, it is encouraging that with only 10 minutes observation per source, at least 35% of all sources with S20>10 mJy can be detected and imaged with global 6 cm VLBI. 相似文献
13.
D. C. Gabuzda P. YU. Kochenov R. I. Kollgaard T. V. Cawthorne 《Monthly notices of the Royal Astronomical Society》2000,315(2):229-240
Total intensity and polarization λ =6 cm Very Large Array (VLA) and global very long baseline interferometry (VLBI) images of the quasar 0917+624 and the BL Lacertae object 0954+658 (both at epoch 1991.43) are analysed. Integrated measurements using the VLA during the VLBI observations indicated that, although there were no substantial total intensity variations, there were significant polarization variations for both sources during the 24-h VLBI experiment. The VLBI data were divided into 2–3 h segments in order to try to identify corresponding rapid variability in the VLBI structure. This analysis revealed intraday variability (IDV) in the VLBI core of 0917+624: both the polarized flux and the polarization position angle varied substantially on time-scales of ∼5–10 h. There is evidence that the VLA polarization variations for 0954+658 occurred in an inner VLBI jet component, where the polarized flux varied by ∼30–40 per cent on time-scales of ∼2 h. 0917+624 and 0954+658 were observed together with 0716+714, an object that also displayed IDV in the polarized flux density measured during our experiment (analysed in a separate paper). These three sources were targeted for the VLBI observations since they had been previously identified as intraday variables, but we had no way of knowing whether they would vary during our observations. The fact that all three exhibited IDV in polarization (but not in total intensity) during our experiment suggests that polarization IDV occurs frequently in at least some IDV sources. 相似文献
14.
We used the VLBA(NRAO, USA) and made VLBI observations towards the compact steep spectrum sources 3C43, 3C48 and 3C454 at the central frequency 1.6 GHz, and obtained their total flux density maps and information on the structures of their components. By comparison with the previous data, we analyzed the variations of their flux densities as well as the displacements of their components. It is found that the total flux density of the source 3C43, as well as the flux densities and relative positions of its components are quite stable in 14 years. For the source 3C454, the total flux density and the flux densities of its components are also relatively stable, but two of the components moved away from the central core with superluminal velocities of 21.6c and 17.7c. Fitted to their flux densities at 4 L-band frequencies, the spectral indexes of the sources 3C43 and 3C454 were obtained to be 0.63 and 0.86, respectively, in good agreement with previous results, and consistent with the definition of α ≥0.5 for compact steep spectrum sources. 相似文献
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I. A. G. Snellen R. T. Schilizzi H. J. van Langevelde 《Monthly notices of the Royal Astronomical Society》2000,319(2):429-444
We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of a sample of faint gigahertz peaked spectrum (GPS) sources selected from the Westerbork Northern Sky Survey. The 5-GHz observations involved a global array of 16 stations and yielded data on the total sample of 47 sources. A subsample of 26 GPS sources with peak frequencies and/or peak flux densities was observed with the VLBA at 15 GHz. A second subsample of 29 sources, with was observed at 1.6 GHz using a 14-station global VLBI array. In this way, 44 of the 47 sources (94 per cent) in the sample were observed above and at or below their spectral peak. Spectral decomposition allowed us to identify three, 11, seven and two objects as compact symmetric objects, compact doubles, core–jet and complex sources, respectively. However, many of the sources classified as compact double or core–jet sources show only two components making their classification rather tentative. This may explain why the strong morphological dichotomy of GPS quasars and galaxies found for radio-bright GPS sources is not as clear in this faint sample. 相似文献
17.
基于磁盘的新型VLBI终端系统--MK5A终端系统 总被引：2，自引：0，他引：2
阐述了国内外VLBI终端系统的发展历史；介绍了MK5A终端系统的概况、工作原理、工作模式和数据模式；展望了下一代VLBI终端系统MK5B和e-VLBI． 相似文献
18.
《New Astronomy Reviews》2002,46(2-7):263-271
We review the question of the age of Compact Symmetric Objects (CSOs); defined as lobe-dominated sources smaller than 1 kpc in overall size. We show that the evidence increasingly points to these objects being very young (<104 yr old). Evidence from spectral aging, energy supply arguments and, most convincingly, from long term VLBI kinematic studies, is all consistent with the ‘youth’ scenario for CSOs. From VLBI kinematic studies hotspot advance speeds in CSOs are found to be 0.1 to 0.3c and external densities estimated from ram pressure balance are ≈1 cm−3. The separate question of the subsequent evolution of CSOs and whether they are the progenitors of classical double sources is, in contrast, not yet definitively answered. However it is found that the numbers of CSOs in flux limited samples is to first order what would be expected under such a scenario. The detailed differences in CSO population density between the data and model predictions might be resolved in various ways. Possibly not all CSOs evolve into large sources, or some sources show recurrent activity or, most likely, the simplest source evolution models need modification. 相似文献
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T. W. B. Muxlow P. N. Wilkinson A. M. S. Richards K. I. Kellermann E. A. Richards M. A. Garrett 《New Astronomy Reviews》1999,43(8-10)
42 hours of A-array VLA data and 18 days MERLIN data at 1.4 GHz have been combined to image a 10 arcminute field centred on the Hubble Deep Field (HDF). This area encloses both the Hubble Deep and Flanking Fields. A complete sample of 87 sources have been detected with flux densities above 40 μJy. All these have been imaged with the MERLIN+VLA combination to produce images with 0.2, 0.3 and 0.5 arcsecond resolution. These are the most sensitive 1.4 GHz images yet made with rms noise levels of 3.3 μJy/beam in the 0.2 arcsecond images. About 70% of the microJy sources are found to be starburst type systems associated with major disk galaxies in the redshift range 0.4–1. Some 20% are found to be low-luminosity AGN systems identified with field ellipticals at redshifts close to 1. The remaining 10% are associated with optically faint systems close to or beyond the HDF limit; many of these may be dust-shrouded starbursts at high redshift. We propose to extend this study to include VLBI data of comparable sensitivity to investigate the compact radio structures found in the microJy source population. 相似文献
20.
We present maps and astrometric results from first epoch, simultaneous MERLIN and Global VLBI observations of the very weak core of a double-lobed radio source, using as reference the bright, compact, flat-spectrum quasar 1636+473 A, 20 arcsec away. The observations were made in May 1995 at 5 GHz. The phase-referenced VLBI map of the weak core, of resolution 1.5 mas, contains a high percentage of the core flux density seen in the MERLIN map. Further hybrid mapping iterations reveal a faint, one-sided core extension on the same side as the MERLIN jet. We explore the effect of both temporal and other coherence losses on the phase-reference map. We relate our results to the structural asymmetry in weak AGN cores within the context of unification models. 相似文献