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  • 1
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    Supernova 1987A - A radiosphere resolved with VLBI five days after the neutrino burst (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The results of VLBI observations of SN1987A are reported. No emission from the supernova above a level of about 20 percent of the supernova's total flux density was detected, although signals were detected from two calibrator sources with amplitudes roughly equal to those determined in earlier VLBI observations. It is inferred that the supernova's radiosphere was resolved, and a lower bound on the radiosphere's radius of 2.2 mas is estimated from an epoch 5.2 days after the neutrino burst. Given the photometric data from the supernova, a distance to the LMC of 50 + or - 5 kpc, and an apparent expansion velocity that varied systematically with time from 18,000-16,000 km/s, as estimated from the blue-shifted H-alpha absorption lines on the days preceding the observations, it is concluded that 5.2 days after the neutrino burst the supernova's radiosphere was at least 2.5 times larger than the inferred blackbody photosphere, and at least as large as the H-alpha line-forming region.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 334; 412-415
    Format: text
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  • 2
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    VLBI observations of the compact components in M82 (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: VLBI observations at 2.3 and 8.4 GHz of 15 compact components in M82, obtained on May 19, 1983, are examined. Angular sizes and linear sizes of the compact sources in M82 are estimated; it is detected that most of the compact sources studied have linear sizes in excess of 0.3 pc. The brightness distribution of the strongest of the 15 compact sources, 41.9 + 58, is investigated; two dominant, elongated components oriented at an angle of about 20 deg and having maximum dimensions of 10-30 mas are observed.
    Keywords: ASTROPHYSICS
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  • 3
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    Quasar 4C39.25 is not contracting (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A map has been made of the quasar 4C39.25, which has been described as consisting of two components whose angular separation remains constant at about 2 marc-sec, using VLBI observations made at 3.6 cm during 1983. From the map it is concluded that Shaffer's (1984) suggestion that this source may have been contracting superluminally during 1979-82 is not correct. Three distinct components are found in the quasar structure, two separated by 2.0 marc-sec and a third, presumably new and not previously reported, situated between the other two. It is possible either that the third component is stationary and that its flux density has rapidly increased to render it visible, or that it has recently been ejected from the westernmost component.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 314; 424
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  • 4
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    The quasars 1038 + 528 A and B (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of VLBI observations of the quasars 1038 + 528 A and B at 2.8, 3.6, 13, and 18 cm at various times between November 1979 and March 1981 are reported. The observations and data calibration are described, as are the mapping and astrometric techniques applied in the study. Both quasars are found to have 'core-jet' morphologies. The core of the A quasar dominates its morphology at centrimetric wavelengths with the brightness temperature of its 400 pc long jet being about 1/100 that of the core. By contrast, the 'jet' in the B quasar is very short (about 70 pc); the tail of this jet has the steepest spectral index found to date in extragalactic compact sources, indicating that high electron losses are responsible for the shortness of the jet. No evidence for appreciable morphological change in the B quasar was found over the time span of the study, whereas a new feature may be emerging from the A quasar core at superluminal speed.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 142; 1 Ja
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  • 5
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    VLBI observations of the 0957 + 561 gravitational lens system (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A series of VLBI observations of the gravitational lens system 0957 + 561 at a wavelength of 13 cm has yielded the positions of the A and B images, the relative magnification of their largest discernible radio structures, and the time variability of their smallest discernible radio structures. These observations have also allowed upper limits to be placed on the flux density of an expected third image. The positions and relative magnification of the A and B images provide new information with which to constrain models of the lens that forms the images. The detection of variations in the flux densities of the cores of A and B suggests that observations at shorter wavelengths may reveal superluminal motion, which may in turn provide a means to measure the relative time delay.
    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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  • 6
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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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  • 7
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    VLBI observations of 23 hot spots in the starburst galaxy M82 (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The simultaneous 2.3 and 8.4 GHz VLBI observations of 23 hot spots in the nuclear region of M82 presented indicate the presence of six hot spots at 2.3 GHz, but only one at 8.4 GHz. Attention is given to a mapping of the brightest hot spot, 41.9+58, at 2.3 GHz, which exhibits a complex brightness distribution whose angular width in the NE-SW direction is 45 mas at the 10-percent contour. These data are consistent with the hot spots in M82 being powerful SNRs, with ages between about 10 and 300 yr.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 323; 505-515
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