Abstract

During its burst of intraday variation (IDV) in June 1996 quasar PKS 0405–385 exhibited rapid changes in the Stokes parameters Q and U that were even faster than the 1 hr timescale changes in I. Auto- and cross-correlation analyses of I,Q, and U at 8.6 GHz show systematic relations between the variations in I,Q, and U. These are well modelled by interstellar scintillation (ISS) of a 14 × 20 μ as source, with about 180 degree rotation of the polarisation angle along its long dimension. This success in explaining the remarkable IDV in polarisation confirms that ISS gives rise to the IDV in this quasar.