The Physics of Pulsar Scintillation

Scintillation is a well-known phenomenon in astronomy, e.g. twinkling of stars due to scattering in the Earth's atmosphere, and variability of compact radio sources due to scattering in the ionosphere and the solar wind. These examples correspond to the so-called regime of weak scattering. Radio pulsars scintillate as a result of scattering in the ionized interstellar medium, but in contrast to the previous cases, the physical regime corresponds to strong scattering. Pulsars exhibit two distinct kinds of variability, called diffractive scintillation and refractive scintillation, on timescales of minutes and weeks respectively. The physics of the various regimes of scintillation are reviewed, and some basic theoretical results are summarized. The properties of imaging in the presence of strong scattering are also discussed.