Emergence and disappearance of micro-arcsecond structure in the scintillating quasar J1819+3845

TL;DR

This study investigates the sudden appearance and disappearance of micro-arcsecond scale structures in the scintillating quasar J1819+3845, revealing dynamic changes in source structure and interstellar scattering properties over time.

Contribution

It provides the first evidence of transient micro-arcsecond structures in a quasar and estimates the scattering screen distance and turbulence level responsible for scintillation.

Findings

Emergence of 15-minute scale structures in 2004-2005

Estimated scattering screen distance of ~3.8 pc or ~2.0 pc

Turbulence in scattering material is exceptionally high

Abstract

The 4.8 GHz lightcurves of the scintillating intra-day variable quasar J1819+3845 during 2004-5 exhibit sharp structure, down to a time scale of 15 minutes, that was absent from lightcurves taken prior to this period and from the 2006 lightcurves. Analysis of the lightcurve power spectra show that the variations must be due to the emergence of new structure in the source. The power spectra yield a scattering screen distance of 3.8 +/- 0.3 pc for a best-fit v_ISS=59 +/- 0.5 km/s or 2.0 +/- 0.3 pc for the scintillation velocity reported by Dennett-Thorpe & de Bruyn (2003). The turbulence is required to be exceptionally turbulent, with C_N^2 > 0.7 Delta L_pc^{-1} m^{-20/3} for scattering material of thickness Delta L_{pc} pc along the ray path. The 2004 power spectrum can be explained in terms of a double source with a component separation 240 +/- 15 microas in 2004.