Radio-wave propagation in the non-Gaussian interstellar medium

Abstract

Radio waves propagating from distant pulsars in the interstellar medium (ISM), are refracted by electron density inhomogeneities, so that the intensity of observed pulses fluctuates with time. The theory relating the observed pulse time-shapes to the electron-density correlation function has developed for 30 years, however, two puzzles have remained. First, observational scaling of pulse broadening with the pulsar distance is anomalously strong; it is consistent with the standard model only when non-uniform statistics of electron fluctuations along the line of sight are assumed. Second, the observed pulse shapes are consistent with the standard model only when the scattering material is concentrated in a narrow slab between the pulsar and the Earth. We propose that both paradoxes are resolved at once if one assumes stationary and uniform, but non-Gaussian statistics of the electron-density distribution. Such statistics must be of Levy type, and the propagating ray should exhibit a Levy flight. We propose that a natural realization of such statistics may be provided by the interstellar medium with random electron-density discontinuities. We develop a theory of wave propagation in such a non-Gaussian random medium, and demonstrate its good agreement with observations. The qualitative introduction of the approach and the resolution of the anomalous-scaling paradox was presented earlier in [PRL 91, 131101 (2003); ApJ 584, 791 (2003)].

27 pages, changes to match published version

References in corpus (4)

• Multifrequency Observations of Radio Pulse Broadening and Constraints on Interstellar Electron Density Microstructure
• Interstellar Turbulence II: Implications and Effects
• Levy model for interstellar scintillations
• Scaling Relations for Turbulence in the Multiphase Interstellar Medium

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• Lévy Flights and Leaky Boxes: Anomalous Diffusion of Cosmic Rays
• On the role of stochastic Fermi acceleration in setting the dissipation scale of turbulence in the interstellar medium
• Noise-Assisted Metastability: From Lévy Flights to Memristors, Quantum Escape, and Josephson-based Axion Searches