Circular polarization in PKS 1519-273
The intra-day variable BL Lac PKS 1519-273 exhibits variations at centimeter wavelengths in total intensity, linear polarization, and circular polarization. The variability is caused by scintillation due to the interstellar medium. PKS 1519-273 displays 4% circular polarization at 4.8 GHz and the variability has persisted as long as the source has been observed. We present observations of this source over several years, showing that the circularly polarized emission is highly variable on micro-arcsecond scales. We determine structural properties of the emission by examining the light curves and associated scintillation theory.