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A. L. Fey (U.S. Naval Observatory), K. M. Desai (No Affiliation)
We report results of multi-frequency VLBA observations of the extragalactic source 2023+336. The line of sight to this source passes through the Cygnus region of the sky. Our new observations confirm the scattered nature of 2023+336 as reported previously by one of us and by other authors. However, the angular size of the source has increased at all observed frequencies by about 50% over observations made just three years prior. We rule out intrinsic structure effects since the source is compact at our highest observing frequency and would contribute negligibly to the measured angular size at our lowest observing frequency (assuming that the intrinsic size scales only as the inverse of the observing frequency). The visibility data at the lowest frequencies show an excess of correlated flux on the longest baselines compared to that expected from a Gaussian image profile. Consistent with the visibility data, the images show significant sub-structure on angular scales smaller than the canonical FWHM angular size of the scattered image. These results are consistent with the "Average Image" regime in which the duration of the observations is short compared to the refractive timescale (the refractive timescale characterizes the largest spatial scales in the scattering screen).