(in collaboration with V. Radhakrishnan)
Extensive monitoring of compact extra-galactic radio sources over the last few decades has revealed many instances of intensity variations of unusual magnitude and duration, termed Extreme Scattering Events. Many models invoking refractive effects due to localized/discrete structures in the ionized component of the ISM have been proposed to explain the observations. These models, however, imply electron density enhancements (as well as pressures) that are 2 to 3 orders of magnitude higher than indicated by other probes.
It is quite possible that the observed effects are not due to any mysterious discrete concentrations, but rather just the combined manifestation of a whole range of hierarchical scales constituting the distribution of the ionized matter. In this paper, we argue that a single power-law description of the electron density distribution in the ISM is consistent with the observations. We also examine the assumptions leading to the earlier estimates of the implied enhancements in the electron density (and pressure) and find no compelling evidence for such over-dense structures. Details of our simulations and results are presented.