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  • Other Sources  (6)
  • 1985-1989  (6)
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Source
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Years
Year
  • 1
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    Strong source VLBI observations at 22 GHz (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Twenty-six strong high-frequency radio sources have been observed at 22.3 GHz on interferometer baselines of approximately 500 million wavelengths. Twenty-five were detected, and 14 have mean visibilities over 50 percent. The strongest sources as a group are more heavily resolved than the weaker sources.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 296; 458-460
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    The Pearson-Readhead Survey from Space (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: The VSOP Space VLBI mission uses the HALCA spacecraft, launched from Japan in February 1997, in conjunction with ground radio observatories around the world to create a high resolution radio-wave length imaging facility. We are using this unique facility to observe a complete sample of Pearson-Readhead Survey sources at 4.8 GHz to determine core brightness temperatures and pc-scale jet properties. The Pearson-Readhead sample has been used for extensive ground-based VLBI survey studies. This sample is ideal for a VSOP survey because the sources are strong, the VSOP u-v coverages are especially good above +350 declination, and multi-epoch ground-based VLBI data and other existing supporting data on these sources exceeds that of any other possible sample. We have chosen to observe a complete subset of this sample that is most likely to show fringes on space-earth baselines. To date we have imaged a majority of the 31 sources in our sample. In addition, we are obtaining matched- resolution 15 GHz observations using the VLBA at epochs close in time to the space VLBI observations to investigate the spectral indices of the source components at high resolution. We gratefully acknowledge the VSOP Project, which is led by the Japanese Institute of Space and Astronautical Science in cooperation with many organizations and radio telescopes around the world. This research was performed in part at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA.
    Keywords: Earth Resources and Remote Sensing
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Relativistic beaming and the nuclei of double-lobed radio quasars (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A complete sample of double-lobed 3CR quasars with minimal orientation bias is defined. Properties of these objects on the greater than kpc scale are consistent with the simple beaming model for their nuclei. VLBI maps of six nuclei reveal 'core-jet' structures. Both nuclei mapped at multiple epochs are modestly superluminal. The distribution of apparent velocities in this sample will provide a stringent test of beaming.
    Keywords: ASTROPHYSICS
    Type: IAU Symposium on the Impace of VLBI on Astrophysics and Geophysics; May 10, 1987 - May 15, 1987; Cambridge, MA; United States
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  • 4
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    A complete sample of double-lobed radio quasars for VLBI tests of source models - Definition and statistics (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A complete, flux-density-limited sample of double-lobed radio quasars is defined, with nuclei bright enough to be mapped with the Mark III VLBI system. It is shown that the statistics of linear size, nuclear strength, and curvature are consistent with the assumption of random source orientations and simple relativistic beaming in the nuclei. However, these statistics are also consistent with the effects of interaction between the beams and the surrounding medium. The distribution of jet velocities in the nuclei, as measured with VLBI, will provide a powerful test of physical theories of extragalactic radio sources.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 98; 1208-122
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  • 5
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    High dynamic range VLBI observations of NGC 6251 (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The large radio galaxy NGC 6251 has been observed with an 11-telescope VLBI array, including the full VLA, at 18 cm. High-dynamic-range maps of both the VLBI-scale and VLA-scale radio structure from these observations, as well as hybrid maps from earlier VLBI experiments at 6 and 13 cm, are presented. The 18-cm VLBI hybrid map has an unusually high dynamic range of about 300 to 1 (ratio of the peak brightness to five times the rms noise level) and is limited by thermal noise rather than calibration errors. A lower limit of 80 to 1 for the ratio of jet/counterjet brightness at parsec scales can be set. This is the strongest such limit produced by VLBI observations of any source to date. If the absence of a detectable counterjet is caused by relativistic beaming, then the jet must be aligned within 45 deg of the line of sight. The VLA map shows a complex structure along the previously detected kiloparsec-scale counterjet. The physical conditions in the inner few parsecs of the NGC 6251 jet and their relation to the conditions in the extraordinarily long and well collimated kiloparsec-scale jets are discussed, and it is shown that both small-scale and large-scale morphology can be explained in terms of a simple model and relativistic beaming.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 305; 684-697
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  • 6
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    Superluminal motion in the double-lobed quasar 3C 245 (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: VLBI observations of 3C 245 obtained at 10.7 GHz with the Mark III array at five epochs in 1981-1986 are reported. The data-reduction and model-fitting procedures are explained, and the results are presented in tables, graphs, and maps along with previously published data on 11 other superluminal sources. The central component of the quasar is found to have an apparent transverse velocity of (3.1 + or - 1.4) c/h, assuming H0 = 100h km/s Mpc and q0 = 0.5. From the apparent source orientation (based on R, variability, apparent curvature, and projected linear size) it is inferred that the apparent transverse velocity is anticorrelated with the angle to the line of sight, as predicted by relativistic-beaming models of superluminal motion.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 321; L11-L15
    Format: text
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