A VLBI view on the extreme scintillator J1819+3845

Scintillation of flat spectrum radio sources provides a unique instrument to study the characteristics of the electron density distribution throughout the interstellar medium as well as to study the microarcsecond structure of compact radio objects. During the course of its extreme activity, the quasar J1819+3845 has been observed with a number of VLBI arrays. The fast variability, up to 600% in less than one hour, has made it very difficult to image the source. The variability has now stopped and we will present scintillation-free VLBI images of J1819+3548 taken with the EVN (2008) and VLBA (2007). We will compare the quiescent phase of J1819+3845 with images of the source during its extreme variability (observed with global and space VLBI). A description of the possible scattering screen and implications for the source internal structure will be presented.Space EngineeringAerospace Engineerin