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  • ASTRONOMY  (3)
  • SPACE SCIENCES  (3)
  • 1
    Publication Date: 2019-06-27
    Description: Both average and individual pulse polarization measurements at 430 MHz are presented for three pulsars: PSR 0823 + 26, PSR 0834 + 06, and PSR 2303 + 30. In each case, the average Stokes parameter waveformes are found to depend on the individual pulse polarization properties in a complicated manner. The average waveforms are in general depolarized by pulse-to-pulse fluctuations in polarization state at a given longitude. Two of the three objects exhibit variations of both linear and circular polarization which are associated with quasi-periodic subpulse modulation phenomena in a manner similar to that reported for linear polarization in PSR 0809 + 74 by Taylor et al. (1971.).
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 188; Mar. 15
    Format: text
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  • 2
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: An investigation of the intensity fluctuations of 28 pulsars near 0.4 GHz indicates that spectra of interstellar scintillation are consistent with a Gaussian shape, that scintillation indices are near unity, and that the scintillation bandwidth depends linearly on dispersion measure. Observations at cm wavelengths show that the observer is in the near field of the scattering medium for objects with the lowest dispersion measures, and confirm the steep dependence of correlation bandwidth on dispersion measure found by Sutton (1971). The variations of scattering parameters with dispersion measure may indicate that the rms deviation of thermal electron density on the scale of 10 to the 11th cm grows with path length through the galaxy.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics; 43; 3, Oc; Oct. 197
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  • 3
    Publication Date: 2019-06-27
    Description: An analysis of pulsar average waveforms at radio frequencies from 40 MHz to 15 GHz is presented. The analysis is based on the hypothesis that the observer sees one cut of a hollow-cone beam pattern and that stationary properties of the emission vary over the cone. The distributions of apparent cone widths for different observed forms of the average pulse profiles (single, double/unresolved, double/resolved, triple and multiple) are in modest agreement with a model of a circular hollow-cone beam with random observer-spin axis orientation, a random cone axis-spin axis alignment, and a small range of physical hollow-cone parameters for all objects.
    Keywords: ASTRONOMY
    Type: NASA-TM-X-70917 , X-693-75-138
    Format: application/pdf
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  • 4
    Publication Date: 2011-08-16
    Description: Observations of 12 compact extragalactic sources were made at 2695 and 8085 MHz in order to detect weak intensity fluctuations caused by interstellar scintillation. Pulsar data are used to estimate the parameters of the interstellar medium needed to interpret the measured upper limits in terms of source angular diameters which are much larger than the scintillation cutoff diameter. It is shown that the observed source rms brightness temperatures are less than 10 to the 15th K and 10 to the 14th K at 2695 and 8085 MHz, respectively, making self-absorbed proton-synchroton radiation and high-brightness coherent mechanisms unlikely. If the sources are composed of 'point' components, each source can contain no fewer than 10,000 such components.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 197; Apr. 1
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  • 5
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: The frequency dependence of the parameters of interstellar scattering between 837 and 8085 MHz for the Vela pulsar are consistent with thin-screen models of strong scattering. The magnitudes of the parameters indicate an anomalous turbulence along the path when they are compared with results for other pulsars with comparable column densities of free electrons in the line of sight. This anomaly is due presumably to the Gum Nebula. The decorrelation frequency, appropriately defined, is related to the pulse broadening time by 2 pi as predicted theoretically.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 190; June 15
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  • 6
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    In:  Other Sources
    Publication Date: 2011-08-16
    Description: Time-averaged flux-density spectra of ten pulsars have been obtained on the basis of simultaneous observations at six frequencies between 250 and 8085 MHz. The effects of interstellar scintillation on the accuracy of the measurements are discussed. All of the pulsars exhibited a power-law spectrum at high frequencies with spectral indices between negative 1.6 and negative 3.0. Several of the pulsars show a more positive spectral index at the low-frequency end of the data.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 189; Apr. 1
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