Observations of IntraDay Variable sources with the Effelsberg and Urumqi Radio Telescopes

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR ChinaE-mail: hjl@bao.ac.cnA sample of classical IntraDay Variable (IDV) and IDV candidate sources has been monitoredwith the Urumqi 25m telescope and the Effelsberg 100m telescope. Aim of the project is to inves-tigate the origin of IntraDay Variability, a phenomenon which has been observed in about 30%of flat spectrum radio quasars. Simultaneous Effelsberg-Urumqi observations demonstrated thatthe Urumqi antenna, although relatively small in diameter, is well suitable for IDV experiments.A few Urumqi datasets, however, turned out to be affected by a spurious ˘24 hours modulation,an effect which has been removed by means of a new procedure for data reduction. In about 14months, 12 epochs of observation have been collected, for a total observing time of more than 45days. The epochs are regularly distributed over the whole year, in order to check for the presenceof systematic annual changes in the variability time scales - a crucial test for verifying the con-sistency of source-extrinsic models of the variability. Preliminary time-analysis of the monitoredsources revealed some hint for a slowing down of the characteristic time scales of S5 0716+714,a result that, if confirmed, would be compatible with a source-extrinsic origin of the variability, incontrast to previous IDV studies. No significant modulation of the time scales has been detectedfor S4 0954+658.Bursts, Pulses and Flickering:Wide-field monitoring of the dynamic radio skyJune 12-15 2007Kerastari, Tripolis, Greece