Session 117 - Galactic ISM.
Oral session, Thursday, January 16
Harbour B,

## [117.06] Radio Scintillation Due to Discontinuities in the Interstellar Plasma Density

H. Lambert, B. Rickett (U. California San Diego)

We develop the theory of interstellar scintillation as caused by an irregular plasma having a power-law spatial density spectrum with a spectral index of \beta = 4 corresponding to a medium with abrupt changes in its density. An outer scale'' is included in the model representing the range over which the density of the medium remains uniform. Such a spectrum could be used to model plasma shock fronts in supernova remnants. We investigate and develop equations for pulse broadening, decorrelation bandwidth of diffractive scintillations, and the refractive scintillation index and compare our results with pulsar measurements. We consider both a medium concentrated in a thin layer and an extended irregular medium. We conclude that the \beta = 4 model gives satisfactory agreement for many diffractive measurements, but that for the refractive scintillation index, it gives less satisfactory agreement than does the Kolmogorov turbulence spectrum. We propose to investigate a composite spectrum, featuring a uniform background turbulence with randomly distributed discrete objects, as modelled by the \beta = 4 spectrum.