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**Session 46 - Interstellar Scattering and Scintillation as Tools in Radio Astronomy.**

*Topical, Oral session, Tuesday, June 09*

*Sierra/Padre, *

## [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
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