Properties of the Scattering Screen in Front of Scintillating Quasar PKS 1257-326

PKS 1257-326 is a quasar showing extremely unusual, rapid interstellar scintillation (ISS), which has persisted for at least a decade. Simultaneous observations with the VLA and ATCA, combined with ATCA monitoring over several years, have revealed some properties of the turbulent ionized medium responsible for the ISS of PKS 1257-326. The scattering occurs in an unusually nearby (~10 pc), localized "screen". The scintillation pattern is highly anisotropic with axial ratio more than 10:1 elongated in a northwest direction on the sky. Recent findings and implications for small-scale ionized structures in the ISM are discussed.