Refractive Focusing by Interstellar Clouds and the Rapid Polarization Angle Swing in QSO 1150+812

摘要

A very rapid polarization position angle swing of～180°(with a time scale of～6 hours)observed at 2cm in QSO 1150+812(z=1.25)was reported by Kochenov & Gabuzda.This very rare event is difficult to explain.We found a pos- sible interpretation in the framework of a source model consisting of three polarized components,in which two compact polarized components are nearly simultaneously occulted by an interstellar cloud,with consequent focusing-defocusing effects.A spe- cific plasma-lens model is proposed which can reasonably fit the polarized flux density curve with results derived for the two lensed components.Some physical parameters of the plasma-lens and the source components are estimated.The two compact po- larized components are estimated to have brightness temperatures of～6×10^(12)K. Thus a bulk relativistic motion with a Lorentz factor less than 10 is required to meet the inverse-Compton limit.