Diffractive scintillation in J1819+3845: how low can you go?
                J-P Macquart & A.G. de Bruyn

We have now observed diffractive scintillation in the IDV quasar J1819+3845
at 21cm for over a year.  Applying the standard theory of diffractive
scintillation to the scintillation characteristics, we deduce that a
compact component of the source must possess a size less than ~5
microarcseconds, with an embarrassingly high brightness temperature in
excess of 10^15 K.  I explain how the scintillation characteristics force
us towards this number, and to what extent we might bring it down by
appealing to special scattering circumstances.