Refractive interstellar scintillation in pulsar dynamic spectra

摘要: The evolution of the dynamic spectra eight pulsars over 16 months is reported. Observations were made at Jodrell Bank 408 MHz from 1984 September to 1986 January. changing form interpreted as refractive modulation diffractive interstellar scintillation. correlation function versus time and frequency was computed for each observation estimates apparent decorrelation widths in time, drift rate scintillation features. A model developed how these three parameters vary with epoch under angles refraction. successfully describes variations four pulsars, which shows some sign reversals between epochs. Two kept a constant rate, we interpret due persistent refracting structures their lines sight, are consistent an intervening H ii region. Studies variability bandwidth, visibility drifting features spectra, shifts speed estimated diffraction pattern. These quantities mostly agree expectations model. pulsar PSRB2016+28, has unusually low proper motion, clear pattern by Earth's annual motion. In 11 epochs observed two showed unmistakable periodic spectra. Several other exhibited occasional patterns modulation. phenomenon varies substantially being more common lower strengths scattering.