Observations of diffractive interstellar scintillation phenomena Available to Purchase

Recent observations of radio source angular broadening and pulsar dynamic spectra are reviewed, with the goal of determining the spectrum of the interstellar density irregularities and the sources which generate the turbulence. Measurements of angular broadening and certain aspects of pulsar dynamic spectra favor ‘‘quasi‐Kolmogoroff’’ density spectra, which are power law with an index less than four. However, pulsar dynamic spectra frequently display phenomena such as drifting bands or quasi‐periodic structures which seem to require spectra with more power at long wavenumbers than can be supplied by quasi‐Kolmogoroff spectra. The resolution of this seemingly contradictory situation is not obvious at the present time. Observations of angular broadening of extragalactic sources and spectral corrugation of pulsars show that the intensity of turbulence in the interstellar medium must be highly spatially inhomogeneous. The paper concludes with suggestions for future observations.