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Multi-frequency Phase Referencing VLBI Observation

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.

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Multi-frequency Phase Referencing VLBI Observation

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  1. 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 2009 18-20 March 2009 KOREA

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

  3. 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 natureof 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 East Asian VLBI Workshop 2009 18-20 March 2009 KOREA

  4. Dual-Freq. Simultaneous Observation • 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 • 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 ANRAO512 • 43 GHz with Beam B3C345 • Separation Angle < 0.5 degree East Asian VLBI Workshop 2009 18-20 March 2009 KOREA

  5. 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)

  6. Phase Solution Analysis ~ 5.5 Hours East Asian VLBI Workshop 2009 18-20 March 2009 KOREA

  7. 0.99 0.98 0.97 Phase Solutions 0.99 0.99 0.95

  8. Phase Solution Analysis connected phases differential phases East Asian VLBI Workshop 2009 18-20 March 2009 KOREA

  9. Phase Referenced Image Imaging for weak sourcesat mm wavelength VLBI

  10. UV coverage (43GHz)

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

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

  13. Images The FIRST phase referenced imagefrom the 22 & 43 GHz simultaneousdual-frequency observation NRAO512 (22GHz) phase model 3C345 (43GHz) original 3C345 (43GHz) phase referenced

  14. Multi-Frequency Phase Referencing Model 22GHz (NRAO512) 43GHz (3C345) Amplitude Calibration Amplitude Calibration Manual Phase Cal Manual Phase Cal Phase Referenced Image (43GHz, 3C345) FRING Global Fringe Fitting Phase Solution Phase SolutionTransfer East Asian VLBI Workshop 2009 18-20 March 2009 KOREA

  15. Phase Solution Transfer Phase Solutionat Lower Freq. (fringe fitting) Phase Connection solve 2pi ambiguity Phase Scaling multiply the freq. ratio Phase Offset Correction modify phase offsets East Asian VLBI Workshop 2009 18-20 March 2009 KOREA

  16. 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

  17. Visibility Phase Offset Frequency Converted Visibility Phase Offsets between Scans

  18. Phase Offset Correctionby Fringe Fitting (solint=20min)

  19. Phase Offset Correctionby modifying SN table

  20. NRAO512 (22GHz) phase model 3C345 (43GHz) original 3C345 (43GHz) phase referenced rms = 0.00194313 peak amp = 0.46 (Jy/beam) rms=0.00298943 peak amp = 1.42 (Jy/beam) rms = 0.0033645 peak amp = 1.39 (Jy/beam)

  21. 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

  22. 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

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

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