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  • 1
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    VLBI observations of the nucleus of the radio galaxy Cygnus A (1981)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The central component of the radio galaxy Cygnus A has been observed in several (very long baseline interferometry) experiments between 1975 and 1979, and the results have been combined to derive a model for the brightness distribution. Some 65% of the nuclear emission appears to come from a compact core. The remaining flux density comes from a more extended region (or regions) up to 4 or 5 mas away lying along a position angle near 100 deg, which is close to that of the extended lobes. Evidence that compact central components reflect the collimation and transport of energy to the outer lobes of radio galaxies is discussed, and several interpretations of the observed asymmetries are considered.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 97; 1, Ap; Apr. 198
    Format: text
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  • 2
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    Time-dependent radio fine structure of the compact sources NRAO 150 and 4C 39.25 (1980)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Very long baseline interferometer observations at 7.85 GHz have been used to probe the milliarcsecond structure of the unidentified, very compact radio source NRAO 150 and QSO 4 C 39.25. NRAO 150 exhibited no structural variations from 1972 to the end of 1974. A model with two circular Gaussian components fits the data well. NRAO 150 had a flux density of 7.6 plus or minus 0.5 Jy in the compact component; 4 C 39.25 showed a two-component structure, the components having a separation of (2.02 plus or minus 0.05 arc sec) x 10 to the -3rd power. The upper bound on the speed of transverse separation is 0.0001 arc sec per year or less than 2.7 c. From the spectrum there are also indications of a third, larger component.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 86; 3, Ju; June 198
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  • 3
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    The very flat radio spectrum of 0735 plus 178 - A cosmic conspiracy (1980)
    In:  Other Sources
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    Publikationsdatum: 2019-06-27
    Beschreibung: Multifrequency interferometric and total flux density measurements of the radiation from 0735 plus 178 are discussed. It is shown that it is far more likely that the very flat radio spectrum of this source results from a superposition of incoherent synchrotron radiation from four distinct, homogeneous components, each with a peaked spectrum, than from radiation from a single inhomogeneous component.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 238
    Format: text
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  • 4
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    New results from the Viking relativity experiment (1982)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The predicted general relativistic effect of solar gravity on the round-trip times of electromagnetic signals traveling between earth and Mars has been verified by means of radio ranging to the Viking spacecraft. The ranging measurements were found to be consistent with the predicted increases of up to 200 microsec in the travel times of the signals to within the estimated uncertainty of 0.2%.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Acta Astronautica; 9; Feb. 198
    Format: text
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  • 5
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    Confirmation of a conspiracy - Dual-band VLBI maps of the flat-spectrum radio source 2021 + 614 (1982)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: VLBI observations at 3.6 and 13 cm wavelengths of the flat-spectrum radio source 2021 + 614 reveal two components, separated by about 6.5 + or - 0.6 milli-arcseconds along a position angle of 36 deg + or - 6 deg. The dual-band observations show that the two components have spectral indices of opposite signs, indicating that, as for 0735 + 178 (Cotton et al. 1980), the flat spectrum of 2021 + 614 is a result of the superposition of spectra from individual components, each having a peaked spectrum, presumably due to incoherent electron synchrotron radiation. If this situation is typical, then there is too large a percentage of flat-spectrum sources for the individual components in each to have independent characteristics.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 262
    Format: text
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  • 6
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    The milli-arcsecond images of Q0957 + 561 (1984)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: VLBI observations at 13 cm have detected similar compact radio sources in the A and B images of the quasar QO957 + 561, and the images are noted to contain core components with flux densities of 22 + or - 1 and 18 + or - 1 mJy, respectively. Data from the short Effelsberg-Madrid baseline suggest that additional correlated flux density, distributed over an angular scale of about 20 milliarcsec accompanies both cores. The observed brightness distributions of these cores are related by a linear magnification matrix, consistent with observation of surface brightness, as would be expected for images produced by a transparent gravitational lens. A search was conducted for evidence of additional compact radio structure within a region encompassing the positions of the galaxy G1 and the B image.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 287; 538-548
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  • 7
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    The medium sensitivity survey - A new sample of X-ray sources with optical identifications and the revised extragalactic log N-log S (1984)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Maccacaro et al. (1982) surveyed approximately 50 sq deg in different regions of the sky at medium sensitivity flux levels intermediate between the Uhuru/Ariel V limit and the Einstein deep survey limit. This 'first' medium sensitivity survey (MSS 1) was primarily aimed at the analysis of the source-count relation for extragalactic X-ray sources. The present investigation is concerned with an extension of the MSS 1 on the basis of an analysis of new fields obtained with the aid of the Imaging Proportional Counter (IPC) on board the Einstein Observatory. A parallel optical program to identify all the new sources was also undertaken. X-ray and optical data are presented for this 'second' complete sample of medium sensitivity survey X-ray sources (MSS 2). The log N-log S relation is derived and discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 283; 495-511
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  • 8
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    Fine time structure in the 1979 March 5 gamma ray burst (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Data on the impulsive phase of the 1979 March 5 gamma ray burst, taken by three identical detectors aboard the Prognoz 7, Venera 11, and Venera 12 spacecraft with 2 ms time resolution, are presented. The first 200 ms of the time history may be described by an exponential decay with time constant of approximately 120 ms up to approximately 100 ms, and time constant of approximately 30 ms thereafter; at low energies, a pulsating component with a period of approximately 23 ms appears. The data could be consistent with torsional vibrations of a neutron star, the rotation of a rapidly spinning neutron star, or oscillations caused by interactions between hot plasma and a magnetic field.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 126; 2 c; 400-402
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  • 9
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    The Einstein Observatory Medium Sensitivity Survey - Optical identifications for a complete sample of X-ray sources (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: It is suggested that virtually all the X-ray sources in the Einstein Observatory's Medium Sensitivity Survey flux range can be identified with objects visible on the POSS, on the basis of the complete identification of all sources north of -25 deg declination. There is no evidence for a significant population of 'blank field' X-ray sources at this flux level, and therefore no evidence for any new X-ray source class with very high L(x)/L(v). Most of the quasars detected in the present survey are spectroscopically similar to optical or radio-selected quasars. About 25 percent of the quasar sample, however, had reddish colors, and permitted lines dominated by a narrow-line component. These objects form a second sequence of active galactic nuclei, distinct in their optical properties from the broad line objects.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 273; 458-477
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  • 10
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    The nucleus of M81 - Simultaneous 2.3 and 8.3 GHz Mark III VLBI observations (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Mark III very long baseline interferometry (VLBI) observations have been made of the nucleus in the normal galaxy M81 (NGC 3031) simultaneously at 2.3 and 8.3 GHz, and it was found that nearly 100% of the flux density of the nuclear region originates in an elongated radio core with linear dimensions 1000-4000 AU, dependent on frequency. This galactic nucleus is the most compact observed in any extragalactic source. The position coincides with that of the nucleus at optical and X-ray wavelengths within the larger uncertainties of the latter two. The position angle of the major axis of the M81 nucleus is within 3 deg of 75 deg at 2.3 GHz and within 6 deg of 50 deg at 8.3 GHz and is frequency dependent at the 4 sigma level. These values straddle the 62 deg position angle of the projection on the sky of the rotation axis of the galaxy. The spectrum of the core is slightly inverted, and the length of its major axis decreases with frequency. These results are consistent with the emission's being incoherent electron synchrotron radiation from an inhomogeneous region with an optical depth varying along the rotation axis of the galaxy.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 262
    Format: text
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