KVN

Multi-frequency Phase Referencing:

with the KVN and beyondR.Dodson1,2

T.H. Jung1,

M. Rioja2,3

KVN, Korea: ICRAR, UWA, Australia: OAN, Spain

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

fastSame sourc

e

43 GHz43 fast

Differentsource

KVN

Basics of new method: SOURCE/FREQ. phase referencing

A,GEO + A,TRO + ST A,STR+nA

A,GEO + A,TRO + ST nA

A,TRO - R * A,TRO = 0

- R * = (R-1/R)

RRA,GEO + A,TRO + ST nA)

RSTR + 2c (D . A,shift) + ST

XR

fast slow

slow

slow slow

…

Target

A,XYZ - R * A,XYZ = 0, Antenna errors cancel!

Frequency Phase Transfer

High:

Low: High:

KVN

Introduce a Second Source B

Basics of new method: SOURCE/FREQ. phase referencing

R 2c (D . B,shift) + ION NST

Source/freq. referenced Visibility phase:

A,STR + 2c D (A,shift - B,shift)

Same as for A

KVN

Important points

• Non-integer ratio between frequencies problematic

(Introduces phase jumps related to phase ambiguities)

…… 2π (nA - nB + R(nA - nB))

• “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)

KVN

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

KVN

43GHz

129GHz

86GHz

22GHz

16MHz x 16CH

IF13 IF14 IF15 IF16

KUS-KYS

Fri

ng

e P

hase

(deg

)Fri

ng

e A

mp

litu

de

(Jy)

IF1 IF2 IF3 IF4 IF5 IF6 IF7 IF8 IF9 IF10 IF11 IF12

1st KVN 4-band Fringes (2012 April)

KVN

Delay

K-band

Rate

K13015aJan 15, 2013

KVN

Delay

Q-band

Rate

K13015aJan 15, 2013

KVN

Delay

W-band

Rate

K13015aJan 15, 2013

KVN

Delay

D-band

Rate

K13015aJan 15, 2013

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

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

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 (±6oC)

KVN

VLBA demonstrations

• 86GHz (relative) phase referencingnot first (Porcas&Rioja) but only practical Measured `core-shifts’ between 43&86 of

<10μasTarget is SiO maser alignment

• 43GHz Absolute Astrometry22 GHz conventional PR + 22/43GHz SFPR

KVN

VLBA demonstrationsFPT: 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

KVN

KVN uv-coverage:

KAVA uv-coverage:

Global uv-cover-age:

Potential to achieve

~40μas with

2mm VLBI

VLBA has long baselines. KVN lacks these

Beyond KVN: Sim. mm-VLBI facili-ties

KVN

Consequence of Adding KVN to VERA

Much greater sensitivity to low(er)surface brightness

KVN And VERA Ar-ray

KVN

Beyond SFPR: MFPR

Can we find the corrections for iono-sphere and

instrumental terms in the data itself? Require ΔTEC → 0

In principle measurements at multiple frequency

Should allow to solve for all the un-knowns:

ΔTECNon-dispersive (Trop)Core-shift

→Measure in delay

→Delay contribution*(k-1)

→Measure in sim. mm freq.

Obs. 4 freqs bracketing FPT observationsLow frequency required: need L band

With~0.1 nsec accuracy get ~0.1 TEC residual

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.