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[78.02] Strong scintillations and Levy flights through the interstellar medium

S. Boldyrev (ITP, Santa Barbara), C. Gwinn (University of California, Santa Barbara)

Temporal broadening of pulsar signals results from electron density fluctuations in the interstellar medium that cause the radiation to travel along paths of different lengths. The Gaussian theory of fluctuations predicts that the pulse temporal broadening should scale with the wavelength as \lambda⁴, and with the dispersion measure (corresponding to distance to the pulsar) as DM². For large dispersion measure, DM>20 pc/cm³, the observed scaling is \lambda⁴ DM⁴, contradicting the conventional theory. Although the problem has existed for almost 30 years, there has been no satisfactory resolution to this paradox.

We suggest that non-Gaussian, intermittent density fluctuations with a power-like probability distribution cause scintillations for distant pulsars. This probability distribution does not have a second moment in a large range of density fluctuations, and therefore the previously applied conventional Fokker-Planck theory does not hold. Instead, we should apply the theory of Levy distributions (so-called Levy flights).

Using the scaling analysis (confirmed by the direct numerical simulations of ray propagation) we show that the observed scaling is recovered for large DM, if the density fluctuations belong to a particular class of Levy distributions. We then theoretically predict the pulse shape arising from these fluctuations and compare it to the observational data.

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.