Frequency-time structure of pulsar scintillation

Slow frequency drifts revealed by multi-channel spectrometer observations of pulsars provide a sensitive method of detecting irregularities of electron density which are too large to cause interstellar scintillation. Observations of four pulsars are used to compare the density variations in the large- and small-scale irregularities. The values obtained are compatible with a Kolmogorov spectrum for scales in the range 1010 to 1013 cm, but suggest that the power-law index may exceed 11/3. The large irregularities offer a simple explanation of apparent reversals in two-station measurements of drift velocity. (author)