1. KVN Multi-frequency Phase Referencing: with the KVN and beyond R.Dodson 1,2 T.H. Jung 1, M. Rioja 2,3 KVN, Korea: ICRAR, UWA, Australia: OAN, Spain

2. KVN Alternative Tropospheric Calibration in mm-VLBI Observe at lower band (e.g. 21.5 GHz) Apply to higher band (e.g. 43 GHz) Conventional Phase referencing to a calibrator source (requirements difficult to meet) Multi-frequency : phase ref. to a lower frequency fast Same source 43 GHz 43 fast Different source

3. KVN Basics of new method: SOURCE/FREQ. phase referencin g A,GEO + A,TRO + ST A,STR + n A A,GEO + A,TRO + ST n A A,TRO - R * A,TRO = 0 - R * = (R-1/R) R R,GEO + A,TRO + ST n A ) R STR + 2 c (D. A,shift ) + ST X R fast slow … Target A,XYZ - R * A,XYZ = 0, Antenna errors cancel! Frequency Phase Transfer High: Low:High:

4. KVN Introduce a Second Source B Basics of new method: SOURCE/FREQ. phase referencing R 2 c (D. B,shift ) + ION NST Source/freq. referenced Visibility phase: A,STR + 2 c D ( A,shift - B,shift ) Same as for A

5. KVN Important points Non-integer ratio between frequencies problematic (Introduces phase jumps related to phase ambiguities) …… 2π (n A - n B + R(n A - n B )) Perfect Tropospheric calibration Direct Astrometric measurement of core-shifts, even at the highest frequencies, > 43 GHz Errors in station coordinates no problem (for cont. VLBI) Frequency agility crucial: VLBA (switching); Best simultaneous observations: KVN (Yebes-40m)

6. KVN 3x 21m Antennas in S. Korea With 4 band simultaneous mm-wave receiver system: 22, 43, 86 & 129 GHz http://kvn-web.kasi.re.kr/en/en_obs_information.php

7. KVN 43GHz 129GHz 86GHz 22GHz 16MHz x 16CH IF13 IF14 IF15 IF16 KUS-KYS Fringe Phase (deg) Fringe Amplitude (Jy) IF1 IF2 IF3 IF4 IF5 IF6 IF7 IF8 IF9 IF10 IF11 IF12 1 st KVN 4-band Fringes (2012 April)

8. KVN DelayK-bandRate K13015a Jan 15, 2013

9. KVN DelayQ-bandRate K13015a Jan 15, 2013

10. KVN DelayW-bandRate K13015a Jan 15, 2013

11. KVN DelayD-bandRate K13015a Jan 15, 2013

12. KVN MFPR applied Visibility Phase @ Q-band (Rate Corrected) MFPR applied with K-band solint 0.1 MFPR applied with K-band solint 0.3 K13015a: Jan 15, 2013 Bad weather at Yonsei

13. KVN MFPR applied Visibility Phase @ W-band (Rate Corrected) MFPR applied with K-band solint 0.1 MFPR applied with K-band solint 0.3 Yonsei W-band v. high Tsys Low SNR at 22GHz

14. KVN MFPR applied Visibility Phase @ D-band (Rate Corrected) MFPR applied with K-band solint 0.1 MFPR applied with K-band solint 0.3 Low SNR at 22GHz Poor temp. control (±6 o C)

15. KVN VLBA demonstrations 86GHz (relative) phase referencing not first (Porcas&Rioja) but only practical Measured `core-shifts between 43&86 of <10μas Target is SiO maser alignment 43GHz Absolute Astrometry 22 GHz conventional PR + 22/43GHz SFPR

16. KVN VLBA demonstrations FPT: Sources track each other FPT: Sources have common residuals SFPR: Phases are at `zero SFPR: Astrometrically corrected phases Image at phase centre Offsets from centre are the position difference btw frequencies

17. KVN KVN uv-coverage: KAVA uv-coverage: Global uv-coverage: Potential to achieve ~ 40μas with 2mm VLBI VLBA has long baselines. KVN lacks these Beyond KVN: Sim. mm-VLBI facilities

18. KVN Consequence of Adding KVN to VERA Much greater sensitivity to low(er) surface brightness KVN And VERA Array

19. KVN Beyond SFPR: MFPR Can we find the corrections for ionosphere and instrumental terms in the data itself? Require ΔTEC 0 In principle measurements at multiple frequenc y Should allow to solve for all the unknowns: ΔTEC Non-dispersive (Trop) Core-shift Measure in delay Delay contribution*(k-1) Measure in sim. mm freq. Obs. 4 freqs bracketing FPT observations Low frequency required: need L band

20. KVN Conclusions: Source Frequency Phase Referencing is now an established method both VLBA and KVN are demonstrating SFPR We are extending into MFPR, and have VLBA observations made. But I have not seen the data yet.