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We have invented a novel technique to measure the radio image of a pulsarscattered by the interstellar plasma with 0.1 mas resolution. We extend the"secondary spectrum" analysis of parabolic arcs by Stinebring et al. (2001) tovery long baseline interferometry and, when the scattering is anisotropic, weare able to map the scattered brightness astrometrically with much higherresolution than the diffractive limit of the interferometer. We employ thistechnique to measure an extremely anisotropic scattered image of the pulsarB0834+06 at 327 MHz. We find that the scattering occurs in a compact regionabout 420 pc from the Earth. This image has two components, both essentiallylinear and nearly parallel. The primary feature, which is about 16 AU long andless than 0.5 AU in width, is highly inhomogeneous on spatial scales as smallas 0.05 AU. The second feature is much fainter and is displaced from the axisof the primary feature by about 9 AU. We find that the velocity of thescattering plasma is 16+-10 km/s approximately parallel to the axis of thelinear feature. The origin of the observed anisotropy is unclear and we discusstwo very different models. It could be, as has been assumed in earlier work,that the turbulence on spatial scales of ~1000 km is homogeneous butanisotropic. However it may be that the turbulence on these scales ishomogeneous and isotropic but the anisotropy is produced by highly elongated(filamentary) inhomogeneities of scale 0.05-16 AU.

100 Microarcsecond Resolution VLBI Imaging of Anisotropic Interstellar Scattering towards Pulsar B0834+06