1995A&A...295...47Q

The structure functions D(τ) of the flux density variations at 2.7GHz and 8.1GHz in the compact radio source 1741-038 (z=1.054) are compared with those at 1.5, 4.9, 15 and 22GHz given by Hjellming & Narayan for a similar observing period. It is shown that for time lags 5≲τ≲30days the structure functions at 2.7GHz and 1.5GHz are very similar and can be approximately represented by a power law D(τ)∝τ^p with index p∼1.7-1.8. The structure functions at 8.1, 15 and 22GHz differ from those at the lower frequencies. A two-component model involving the extended Galactic interstellar medium and a thin screen with enhanced scattering strength is proposed. Using the refractive interstellar scintillation theory, the theoretical structure functions for the six observing frequencies are calculated. It is shown that the observed structure functions at 1.5 and 2.7GHz can be well fitted by the model. The theoretical structure functions for the three higher frequencies (8.1, 15 and 22GHz) are found to be much smaller than the observed structure functions. Thus the high frequency variations can not be fitted within the presently discussed RISS models and are probably intrinsic to the source.