VLBI observations of a pulsar's scattering disk

VLBI observations of the scattering disk of pulsar 1933+16 agree with predictions for a Kolmogorov spectrum of density fluctuations in the interstellar plasma. A novel least-squares fit technique was used to self-calibrate the data and fit models to the visibilities. Solving for the spectral index of density fluctuations, alpha, from the visibility as a function of baseline length, alpha(vis) = 3.52 + or - 0.13 is obtained, consistent with alpha = 11/3 for a Kolmogorov spectrum. The scaling of size with frequency agrees with that predicted on the basis of such a spectrum. An upper limit of 1:1.7 is placed on the elongation of the scattered image.