Intermittency of electron density in interstellar kinetic Alfvén wave turbulence

Abstract

The statistics of electron density fluctuations in kinetic Alfvén wave (KAW) turbulence is investigated in connection with the inferred Lévy statistics of pulsar signal broadening. Using analytic theory and computation, decaying KAW turbulence is shown to form coherent, intermittent current filaments in regions where local current intensity exceeds the rms value by a critical factor of a few. Nonlinear mixing is suppressed because the filament magnetic field has sufficient shear to refract away turbulent waves. While the magnetic field and density associated with the filament are as coherent as the current, they are not localized and isolated. Ampere’s law dictates that the magnetic field decays as r−1 outside the current, and KAW equipartition dictates that density has the same envelope. This structure gives the density gradient a Lévy distribution, consistent with pulsar scintillation.