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Session 46 - Interstellar Scattering and Scintillation as Tools in Radio Astronomy.
Topical, Oral session, Tuesday, June 09

[46.15] On the Theory of Pulse Propagation and Two-frequency Field Statistics in Irregular Interstellar Plasmas

H. C. Lambert (UC San Diego)

Two-frequency second moments and pulse profiles are computed for plane and spherical waves both propagating in an extended plasma and incident on a thin plasma phase screen located between the source and the observer. The various models considered for the electron-density wavenumber-spectrum are the simple power-law model, the power-law model with an inner scale, the ``\beta=4 model,'' and the square-law structure function model. The power-law model with spectral exponent \beta=11/3 corresponds to the Kolmogorov turbulence spectrum. The \beta=4 model suggests the random distribution in location and orientation of discrete objects across the line of sight. An outer scale is included in the \beta=4 model to account for the average size of the objects. The diffractive decorrelation bandwidth, \Delta \nu_d, obtained from the square of the magnitude of the two-frequency second moment, is related to the scattering broadening time, \Delta t_d, via the Fourier uncertainty relation: 2\pi \Delta \nu_d \Delta t_d = C_1. Numerical values for the constant C_1 are computed for the aforementioned geometries and spectral models of the scattering medium. The theoretical pulse profiles reveal similar scattering tails regardless of the distribution of scattering material along the line of sight. Hence measurements of the scattering tails of pulsars may be used to constrain the various spectral models of the galactic electron density fluctuations, independent of the scattering geometry.

Program listing for Tuesday