Vol. 574
In section 4. Extragalactic astronomy

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

by A.G. de Bruyn and J-P. Macquart, A&A 574, A125


Understanding the fine structure of plasma turbulence in the interstellar medium has remained a challenge for decades. The best probe is scintillation of strong extragalactic point-like radio sources. Using the combination of frequency and time-domain methods, the authors exploit the rotation measure variations of the source to study the patchiness and dimensions of the local scattering screen along the line of sight to the quasar. The small-scale structure, on the order of 100 AU, derived in this study represents the finest scale definitively discerned in the interstellar medium. The vicinity of the scattering screen, within 3 pc, places it at the borders of the solar neighborhood and probes the turbulence in the diffuse ionized interstellar medium. This is a remarkable data set and a detailed analysis of the intensity and polarization variability induced by the foreground. The derived density and extent make it very likely that the scattering screen is extremely patchy, and provide a strong constraint for testing turbulence modelling in the local ISM.