The intra-hour variable quasar J1819+3845: 13-year evolution, jet polarization structure and interstellar scattering screen properties

Abstract

We examine the long-term evolution of the intra-hour variable quasar, J1819+3845, whose variations have been attributed to interstellar scintillation by extremely local turbulent plasma, located only 1–3 pc from Earth. The variations in this source ceased some time in the period between June 2006 and February 2007. The evolution of the source spectrum and the long-term lightcurve, and the persistent compactness of the source VLBI structure indicate that the cessation of rapid variability was associated with the passage of the scattering material out of the line of sight to the quasar. We present an extensive analysis on the linear polarization variations and their relation to total intensity variations. The proper motion of polarized features in the quasar jet is found to be sub-luminal. Systematic time delays between Stokes I, Q and U, in combination with the structure of the source obtained from 8.4 GHz VLBI data confirm the estimate of the screen distance: 1–2 pc, making the screen one of the nearest objects to the Solar system.