multi-frequency phase referencing: with the kvn and beyond
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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.
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