Non-Gaussian Radio-Wave Scattering in the Interstellar Medium

Abstract

It was recently suggested by Boldyrev & Gwinn that the characteristics of radio scintillations from distant pulsars are best understood if the interstellar electron-density fluctuations that cause the time broadening of the radio pulses obey non-Gaussian statistics. In this picture the density fluctuations are inferred to be strong on very small scales ($\sim 10^8-10^{10}cm$). We argue that such density structures could correspond to the ionized boundaries of molecular regions (clouds) and demonstrate that the power-law distribution of scattering angles that is required to match the observations arises naturally from the expected intersections of our line of sight with randomly distributed, thin, approximately spherical ionized shells of this type. We show that the observed change in the time-broadening behavior for pulsar dispersion measures $\lesssim 30\mathrm{pc}{\mathrm{cm}}^{-3}$ is consistent with the expected effect of the general ISM turbulence, which should dominate the scattering for nearby pulsars. We also point out that if the clouds are ionized by nearby stars, then their boundaries may become turbulent on account of an ionization front instability. This turbulence could be an alternative cause of the inferred density structures. An additional effect that might contribute to the strength of the small-scale fluctuations in this case is the expected flattening of the turbulent density spectrum when the eddy sizes approach the proton gyroscale.

15 pages, 3 figures, accepted to ApJ

References in corpus (6)

• Multifrequency Observations of Radio Pulse Broadening and Constraints on Interstellar Electron Density Microstructure
• Interstellar Turbulence II: Implications and Effects
• Deflection of Pulsar Signal Reveals Compact Structures in the Galaxy
• The Frequency Evolution of Interstellar Pulse Broadening from Radio Pulsars
• Levy model for interstellar scintillations
• Radio-wave propagation in the non-Gaussian interstellar medium

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• Detection of OH absorption against PSR B1718-35
• 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
• Investigating Extreme Scattering Events by Volumetric Ray-tracing
• Noise-Assisted Metastability: From Lévy Flights to Memristors, Quantum Escape, and Josephson-based Axion Searches