Measuring AGN Core-shift Effect by Extended KVN with Global Baselines

Very Long Baseline Interferometry (VLBI) at millimeter wavelengths results in the highest angular resolutions achieved in astronomy and has a unique access to emission regions that are inaccessible with any other approach or at longer wavelengths. The simultaneous multi-frequency VLBI system in the Korean VLBI Network (KVN) is considered one of the most effective systems for compensating the atmospheric phase fluctuations, which is particularly bothersome at mm-VLBI. We have been demonstrating its performance and uniqueness at mm-VLBI observations. As a results, international VLBI partners from Japan, China, Australia and EU have expressed their interest on the KVN style simultaneous multi-frequency system. In this talk, we will report the activities for extending the simultaneous multi-frequency system to global VLBI network and introduce its science driver, measuring AGN core-shift effects.