A frequency correlation analysis of pulsar scintillation spectra

Frequency autocorrelation functions derived from the observations of pulsar scintillation spectra at 327, 480 and 1416 MHz have been compared with the theoretical functions for the thin-screen and the extended model of the turbulent medium, and for a power law and a Gaussian wavenumber spectrum of the electron density irregularities. In the case of the extended model, improved numerical solutions for the second-order moment of the wavefield have been used. The results confirm an earlier finding that only the steep power-law spectra with the index α > or approx 3.8 give a good agreement with the observations. No difference between the shapes of the observed frequency autocorrelation functions for the low and the high dispersion measure pulsars has been found. In the case of PSR 1933 + 16, the thin-screen approximation appears to fit the data better than the extended model. A significant change in the scintillation pattern of PSR 1133 + 16 within three months has been detected. (author)