A New Limit on the Angular Diameter of Quasar J1819+385 from an
Interstellar Scintillation Arc Analysis

Barney Rickett & Bill Coles (Univ. Calif. San Diego) and J-P Macquart
& Ger de Bruyn (NFRA, Dwingeloo and Kapteyn Inst.  Groningen)

Stinebring et al. (2001) discovered that a 2-D Fourier analysis of the
random-looking dynamic spectra of pulsar intensity scintillation
revealed a remarkably simple pattern of parabolic arcs.  This provides
a powerful new way to characterize the fine structure in the
scintillation, that is particularly sensitive to the angular diameter
of the source.  We have analyzed the rapid flux density variations
(IDV) of Quasar J1819+385 and find no interstellar scintillation arcs
in Westerbork observations near 6 and 20 cm. We have also simulated
the scintillation under the same observing conditions with a range of
models for the source diameter. By comparing the observed and
simulated results we will set limits on the source diameter and
compare them with other estimates from the scintillation modelling in
this quasar.