2 0 0 7 ) 0 2 1 Annual modulation in the IDV timescale of J 1128 + 592

Short time scale radio variations of compact extragalactic radio quasars and blazars known as IntraDay Variability (IDV) can be explained in at least some sources as a propagation effect; the variations are interpreted as scintillation of radio waves in the turbulent interstellar medium of the Milky Way. One of the most convincing observational argu ments in favour of a propagationinduced variability scenario is the observed annual modula tion in the characteristic variability time scale due to the Earth’s orbital motion. So far there are only two sources known with a well-constrained seasonal cycle. J1128+592 is a recently d iscovered, highly variable IDV source. Previous, densely time-sampled flux-density measurements with the Effelsberg 100-m radio telescope (Germany) and the Urumqi 25-m radio telescope (China) , strongly indicate an annual modulation of the time scale. Here, we summarise the annual modu lation model derived using all the measurements, carried out in the last 2.5 years.