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  • 1
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    Polarization distributions in compact radio sources (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Intensity and polarization maps of active galactic nuclei, obtained with marcsec resolution at 5 GHz using the Mark III VLBI array during 1981-1982, are presented. The techniques of high-resolution polarization synthesis are described, and maps for the superluminal quasar 3C345, the superluminal galaxy 3C120, and the BL Lac objects 0735 + 178 and OJ287 are characterized, with an emphasis on the relationship between arcsec-scale and marcsec-scale jets.
    Keywords: ASTROPHYSICS
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  • 2
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    X-ray studies of quasars with the Einstein Observatory. III The 3CR sample (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Using X-ray emission detected by the Einstein Observatory from each of the 33 3CR quasars in Schmidt's complete sample, it is demonstrated that there is a relationship between the X-ray emission and centimeter wavelength radio emission even for steep-spectrum quasars, provided that only the radio emission from the central object is considered. The observations are summarized, and the estimation of the X-ray luminosity distribution, rather narrow compared to the radio and optical luminosity distributions, is presented. The relationship between X-ray and radio emission is discussed, as is the cosmological evolution of the X-ray luminosity function. The relationship between X-ray and optical luminosity provides an explanation for the finding that X-ray selected quasars have lower redshifts than optically selected quasars of the same optical magnitude.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 268; May 1
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  • 3
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    A survey of the milliarcsecond polarization properties of BL Lacertae objects at 5 GHz (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Consideration is given to millarcsecond-resolution total-intensity and linear polarization maps at 5 GHz presented for 11 BL Lacertae objects. In every BL Lacertae object in which polarization structure was detected, the polarization position angle of the knots is nearly parallel to the VLBI structural axis. The direction of the polarization in the cores of these sources appears to be random. The preferred polarization direction in the jets is explained by the fact that plane perpendicular shock waves are common in these sources; the origin of the absence of the preferred polarization direction in the core components is unclear. These results support an early conclusion that it cannot be the case that a significant number of BL Lacertae objects are gravitationally microlensed images of more distant quasars, since the characteristic VLBI polarization structures observed in these two types of objects are very different.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 388; 40-54
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  • 4
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    Is 1308+326 A BL Lacertae object or a quasar? (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The active galaxy 1308+326 (z = 0.996) has been classified as a BL Lacertae object because of its nearly featureless optical continuum and high and variable polarization. New VLBI polarization images of 1308+326, however, show both VLBI polarization structure and tentative superluminal motions that are characteristic of quasars rather than BL Lacertae objects. These data strongly suggest that this source is simply a quasar with emission lines of small equivalent width. We discuss the possibility that the optical continuum is enhanced by microlensing in a foreground galaxy, as suggested by Stickel et al.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 410; 1; p. 39-43.
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  • 5
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    Radio constraints on the nature of BL Lacertae objects and their parent population (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: 5 GHz VLA observations of 17 BL Lac objects with bright radio cores at both high and low resolution are reported. Extended emission is detected around most objects. None of the sources observed at low resolution show evidence of giant halos on the scale of tens of arcmin. In general, the sources with the most luminous extended emission exhibit FR II characteristics in both morphology and polarization, and less luminous sources exhibit FR I characteristics. Thus, the parent population of the BL Lac objects contains both FR I and FR II radio sources. No BL Lac objects are found that clearly exhibit quasarlike polarization at milliarcsec resolution. This argues against the view that the more luminous BL Lac objects are simply an extension of the quasar/OVV population, or that most BL Lac objects are gravitationally microlensed images of distant quasars. Other properties are generally consistent with the view the BL Lac objects are normal radio galaxies whose jets make a small angle to the line of sight.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 104; 5; p. 1687-1705.
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  • 6
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    The structure of protostellar accretion disks and the origin of bipolar flows (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Equations are obtained which govern the disk-wind structure and identify the physical parameters relevant to circumstellar disks. The system of equations is analyzed in the thin-disk approximation, and it is shown that the system can be consistently reduced to a set of ordinary differential equations in z. Representative solutions are presented, and it is shown that the apparent paradox discussed by Shu (1991) is resolved when the finite thickness of the disk is taken into account. Implications of the results for the origin of bipolar flows in young stellar objects and possible application to active galactic nuclei are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 410; 1; p. 218-238.
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  • 7
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    A technique for detecting massive collapsed objects in the dark halo of the Galaxy (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: If the Galaxy possesses a dark halo of massive objects, they will produce small but potentially detectable distortions in the images of distant, extended objects due to gravitational lensing effects. An illustrative analytic and a more realistic numerical model are presented for calculating the number and angular sizes of these distortions, and a specific example of a digital filter is described which could be used for the identification of such distortions. The sensitivity of possible searches for the effect in the image of M31 and the Galactic Center are discussed in some detail. Simulated images of distortions of various angular sizes in these fields as they would be expected to appear in ground-based and Space Telescope CCD frames are presented. A Galactic halo of black holes such as that proposed by Lacey and Ostriker might well be detectable ina practically realizable experiment.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 100; 146-155
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  • 8
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    Origin of the hot gas and radio blobs at the Galactic Centre (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Radio continuum observations have shown a chain of blobs of emission leading from SgrA* to a small cavity which is located in one of the ionized gas streamers (the Bar) that orbit SgrA* and which is associated with hot gas. Further high-resolution radio images are presented here which show that the blobs are connected to SgrA* by a ridge of emission. It is suggested that the blobs are formed by the interaction of stellar winds from the IRS16 cluster with the gravitational potential of SgrA*. The hot gas then results from the dissipation of the kinetic energy of the blobs as they collide with the orbiting ionized streamer. These collisions are of dynamical significance for the motion of the Bar around the Galactic Center, and there should be detectable variability in the structure on a timescale of 10 yrs.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 357; 6376,; 308-310
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  • 9
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    Anisotropy in the angular broadening of Sagittarius A(*) at the galactic center (1994)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: We present the results of a lambda = 20 cm (VLA) squared observation of the compact Galactic center radio source Sgr A(*). The scatter-broadened image is elongated in the east-west direction, with an axial ratio of 0.56 +/- 0.22 and a position angle of 82 deg +/- 1.8 deg. A similar shape and orientation has been found previously at shorter wavelengths using Very Long Base Interferometry (VLBI) and Very Long Baseline Array (VLBA). Both the major and minor axes follow the lambda squared law appropriate for scattering by turbulence in the intervening medium. We argue that the scattering occurs in thin ionized surface layers of molecular clouds lying in the central 100 pc of the Galaxy. The ionized regions are characterized by electron densities of 10(exp 4)/cu cm and milligauss magnetic field strengths, and are responsible for the diffuse free-free emission and the Faraday rotation in the region.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 434; 2; p. L63-L66
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  • 10
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    The linear polarization of 3C 345 at milliarcsecond resolution (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A polarization-sensitive 6 cm map of the superluminal quasar 3C 345 with angular resolution 2.5 x 4.7 mas was made using four stations of the US VLBI network. The optically thick core is essentially unpolarized, while both of the knots in the jet are highly polarized. The inner knot C3 has m = 11 percent at electric vector position angle chi = 22 deg, and the outer knot C2 has m = 6 percent at chi = 83 deg. Thus the magnetic field appears to be parallel to the jet near its base and to change direction down the jet.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 304; L1-L4
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