Compact Intraday Variable Radio Cores: New Observational Approaches

The evidence for refractive interstellar scintillation (RISS) being the main cause for rapid intraday variations (Intraday Variability, IDV) in Quasars and BL Lacs has recently become stronger. If IDV is still a complex composition of extrinsic and source intrinsic effects, the intrinsic part of the IDV pattern should show up in the millimeter and sub-millimeter regime due to the frequency dependence of RISS. Hence, observations at higher frequencies are essential in order to exclude RISS as the sole cause of IDV. Here we report on our new attempt to search for rapid variations at much higher frequencies. In addition, the possibility of a direct detection of the postulated scattering screen in front of IDV sources will be discussed. Our recent line observations towards a few IDV sources lead to the first detection of a high latitude molecular cloud in front of an intraday variable radio core.