Multi-frequency Phase Referencing VLBI Observation - Phase Referenced Image - Tae Hyun Jung, Bong Won Sohn, Hideyuki Kobayashi, Tetsuo Sasao, Tomoya Hirota, Osamu Kameya, Yoon Kyung Choi, Mareki Honma, Hyun Soo Chung East Asian VLBI Workshop March 2009 KOREA

Multi-Freq. Phase Referencing Observation Phase Solution Analysis Phase Solution Transfer Phase Referenced Image Overview

East Asian VLBI Workshop March 2009 KOREA Multi-Frequency Phase Referencing Basic Idea - Using the fringe phase of a source at a lower freq. in order to calibrate the phase of the same source at higher one. - The non-dispersive nature of the water vapor-induced excess path delay in the troposphere over the wide range of radio frequency. Merits – resolve the reference source problem – no loss of coherence for a phase compensation by using the same source without the angular distance btw target and calibrator sources – weak source imaging by longer integration times

Testing the feasibility of the multi- frequency phase referencing Phase solution transfer from lower freq. to higher one Atmospheric delay compensation between 22 & 43 GHz East Asian VLBI Workshop March 2009 KOREA Dual-Freq. Simultaneous Observation The first experiment with a dual-freq. simultaneous observation using VERA Observation –Bandwidth 128 MHz, LL, –Dual Mode Setting –Target Sources 22 GHz with Beam A NRAO GHz with Beam B 3C345 –Separation Angle < 0.5 degree

Dual Mode Setting 3C345 α=16:42:58.8 δ=+39:48:37 beam B (43 GHz) NRAO512 α=16:40:29.6 δ=+39:46:46 beam A (22 GHz)

Phase Solution Analysis East Asian VLBI Workshop March 2009 KOREA ~ 5.5 Hours

Phase Solutions

Phase Solution Analysis East Asian VLBI Workshop March 2009 KOREA differential phases connected phases

Phase Referenced Image Imaging for weak sources at mm wavelength VLBI

UV coverage (43GHz)

Images NRAO512 (22GHz) phase model 3C345 (43GHz) original 3C345 (43GHz) phase referenced

Images NRAO512 (22GHz) phase model 3C345 (43GHz) original 3C345 (43GHz) phase referenced

Images NRAO512 (22GHz) phase model 3C345 (43GHz) original 3C345 (43GHz) phase referenced The FIRST phase referenced image from the 22 & 43 GHz simultaneous dual-frequency observation

Multi-Frequency Phase Referencing 22GHz (NRAO512) 43GHz (3C345) Amplitude Calibration Manual Phase Cal FRING Global Fringe Fitting Phase Solution Phase Solution Transfer Phase Referenced Image (43GHz, 3C345) East Asian VLBI Workshop March 2009 KOREA Model

Phase Solution Transfer Phase Solution at Lower Freq. (fringe fitting) East Asian VLBI Workshop March 2009 KOREA Phase Connection solve 2pi ambiguity Phase Scaling multiply the freq. ratio Phase Offset Correction modify phase offsets

Phase Referenced Images from the Multi- frequency Simultaneous Phase Referencing Good –No need to interpolation btw. phase solutions (e.g. Fast freq. switching by Middelberg) –longer integration time Problems –failed phase solutions  cannot be used –phase connection (solve 2pi problem)  sometimes difficult to resolve –visibility phase alignment  2pi ambiguity btw scans

Visibility Phase Offset Frequency Converted Visibility Phase Offsets between Scans

Phase Offset Correction by Fringe Fitting (solint=20min)

Phase Offset Correction by modifying SN table

NRAO512 (22GHz) phase model 3C345 (43GHz) original 3C345 (43GHz) phase referenced rms = peak amp = 0.46 (Jy/beam) rms = peak amp = 1.39 (Jy/beam) rms= peak amp = 1.42 (Jy/beam)

Summary and Discussion We made a dual-frequency simultaneous observation at 22 & 43 GHz using VERA and analyzed phase solutions to test the feasibility of multi-frequency phase referencing for KVN The phase solutions btw. 22GHz & 43GHz showed a very tight correlation. From the analysis of the Allan standard deviation of the differential phase solutions, the atmospheric phase fluctuations can be compensated effectively by using this method From the 22GHz & 43 GHz simultaneous observation with VERA, we get the first 43GHz phase referenced image and we hope to image many weak sources by multi-frequency phase referencing

Summary and Discussion VLBI Imaging at higher frequencies will be able to have a good chance with multi-frequency phase referencing - AGNs : Core shift, accretion, jet formation, black-holes etc… - Masers : multi-line observation, environmental studies of evolved stars etc… For better imaging capability, KVN+VERA observation is definitely essential

Multi-freq. phase referenced observation between KVN + VERA is coming soon !! KVN VERA Thank You!!