Research in Astronomy and Astrophysics

Abstract There has been great progress recently in the study of radio variabil-ity, including the phenomenon of intraday variability (IDV) which occurs on short timescales of 50 h or less. There are two common explanations for IDV: an intrin-sic mechanism or the effect of radio propagation through the interstellar medium. We consider the case of refractive interstellar scintillation (RISS), an extrinsic cause of radio variability. We theoretically derive the structure function of the ‘thick screen’ RISS model by using an approximation method, and discuss its application to the IDV phenomenon with some simulated results. Finally, the IDV source J1128+5925 is fitted with the ‘thin screen ’ RISS model. Some possible combinations of param-eters, namely source size, distance and relative velocity of the scattering screen, are presented. Key words: radio variable source — refractive scintillation — structure function, IDV