Interstellar scattering of the radio source 2013+370

Results are reported from a six-station 1663-MHz VLBI observation of the radio source 2013+370. The image of this source is dominated by interstellar scattering and is observed to be elliptical, with a major axis (FWHM) of 17 marcsec and an axial ratio of of 0.70. A fit of the observations to a model visibility function yields a value for alpha, the spectral index of the power-law density irregularity spectrum, of alpha=3.79 + or - 0.05. Corrections for the finite angular size of the source would probably produce a downward revision of alpha. The present observations are consistent with the interstellar density spectrum being close to Kolmogoroff for those scales which determine the angular broadening.