Bong Won Sohn

First simultaneous 4-frequency phase referencing test for mm-VLBI observation

We present the results of the first 4-frequency simultaneous VLBI fringe detection at 22, 43, 86, and 129 GHz with the Korean VLBI Network (KVN) along with a multi-frequency phase referencing (MFPR) test. The KVN employed a new multi-frequency receiver system that can observe four different radio bands (22/43/86/129 GHz) simultaneously. This system is expected to be an excellent tool to calibrate the atmospheric phase fluctuations by applying MFPR. 4-frequency simultaneous fringes of 3C279 at 22, 43, 86, and 129 GHz were first successfully detected on all three KVN baselines in April 2012. The tight correlation of fringe phases between the four frequencies is a clear indication of a non-dispersive characteristic of the neutral troposphere to the radio systems. A high signal-to-noise ratio fringe-detection of 3C279 at 129 GHz was obtained by referencing to the 22 GHz fringes. This initial experiment demonstrates the feasibility of MFPR as an effective way to overcome short coherence time in mm-VLBI.

KVN SOURCE-FREQUENCY PHASE-REFERENCING OBSERVATION OF 3C 66A AND 3C 66B

In this proceedings, preliminary results of the KVN Source-Frequency Phase-Referencing (SFPR) observation of 3C 66A and 3C 66B are presented. The motivation of this work is to measure the core-shift of these 2 sources and study the temporal evolution of the jet opacity. Two more sources were observed as secondary reference calibrators and each source was observed at 22, 43, and 86 GHz simultaneously. Our preliminary results show that after using the observations at the lower frequency to calibrate those at the higher frequency of the same source, the residual visibility phases for each source at the higher frequencies became more aligned, and the coherence time became much longer; also, the residual phases for dierent sources, within 10 degrees angular separations, follow similar trends. After reference to the nearby calibrator, the SFPRed maps were obtained as well as the astrometric measurements, i.e. the combined coreshift. The measurements were found to be aected by structural blending eects because of the large beamsize of KVN, but this can be corrected with higher resolution maps (e.g. KAVA maps).

KVN Source-Frequency Phase-Referencing Observation of 3C 66A & 3C 66B

In this proceeding, we present some preliminary results of o ur KVN Source-Frequency PhaseReferencing (SFPR) observation of 3C 66A and 3C 66B. The moti vation of this work is to measure the core-shift of these 2 sources and study the temporal evolution of the jet opacity. The KVN core-shift measurements are found to be affected by inner je t structure blending. We have conducted high resolution imaging observation with KaVA to ove rcome this issue. The measurement with structure correction is much smaller and thus more reas on ble. No significant core-shift variation has been found over two months timescale while the cor position at a single frequency has changed. This may be related to the inner jet structural c hange or real core motion.