multi-frequency phase referencing vlbi observation - phase referenced image - tae hyun jung, bong...

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

Multi-Freq. Phase ReferencingObservation

Phase Solution AnalysisPhase Solution Transfer

Phase Referenced Image

Overview


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


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 NRAO512• 43 GHz with Beam B 3C345

– Separation Angle < 0.5 degree

Dual Mode Setting

3C345α=16:42:58.

8δ=+39:48:3

7

beam B (43 GHz)

NRAO512α=16:40:29.

6δ=+39:46:4

6

beam A (22 GHz)

Phase Solution Analysis


~ 5.5 Hours

Phase Solutions at Mizusawa-Iriki Baseline -1-

Time (sec)

54000 56000 58000 60000 62000

Ph

as

e (

deg

)

-200

-150

-100

-50

0

50

100

150

200

22GHz Phases (NROA512)43GHz Phases (3C345)

Phase Solutions

Connected Phases and Differential Phases

Time (sec)

54000 54200 54400 54600 54800 55000 55200

Ph

ase

(deg

)

0

500

1000

1500

2000

2500

Connected Phase at 22GHzConnected Phase at 43GHzDifferential Phases


Time (sec)

55600 55800 56000 56200 56400 56600 56800

Ph

as

e (

de

g)

-600

-400

-200

0

200

400

600

800



Time (sec)

58800 59000 59200 59400 59600 59800 60000 60200

Ph

ase

(deg

)

-1000

-500

0

500

1000

1500Connected Phase at 22GHzConnected Phase at 43GHzDifferential Phases


Time (sec)

57200 57400 57600 57800 58000 58200 58400 58600

Ph

as

e (d

eg

)

-200

0

200

400

600

800

1000



Time (sec)

60400 60600 60800 61000 61200 61400 61600 61800

Ph

ase

(deg

)

-400

-200

0

200

400

600

800

1000



Time (sec)

62000 62200 62400 62600 62800 63000 63200 63400

Ph

ase

(deg

)

-3000

-2500

-2000

-1500

-1000

-500

0

500

1000


0.99

0.99

0.97

0.95

0.98

0.99

Phase Solution Analysis


differential phases

connected phases

Phase Referenced Image

Imaging for weak sourcesat mm wavelength VLBI

UV coverage (43GHz)

Images

NRAO512 (22GHz)phase model

3C345 (43GHz)original

3C345 (43GHz)phase referenced

Images




The FIRST phase referenced image

from the 22 & 43 GHz simultaneous

dual-frequency observation

Multi-Frequency Phase Referencing

22GHz(NRAO512)

43GHz(3C345)

Amplitude Calibratio

n

Amplitude Calibratio

n

Manual Phase Cal

Manual Phase Cal

FRING Global Fringe Fitting

PhaseSolutio

n

Phase SolutionTransfer

Phase Referenced

Image(43GHz, 3C345)


high high low

low tt

Model

Phase Solution Transfer

Phase Solution at Lower Freq.

(fringe fitting)


Phase Connectionsolve 2pi ambiguity

Phase Scalingmultiply the freq. ratio

1 1( ) highhigh low lown n n

low

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 OffsetFrequency Converted VisibilityPhase Offsets between Scans

Phase Offset Correctionby Fringe Fitting (solint=20min)

Phase Offset Correctionby modifying SN table




rms = 0.00194313 peak amp = 0.46

(Jy/beam)

rms = 0.0033645peak amp = 1.39

(Jy/beam)

rms=0.00298943peak 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. p

hase

referenced observation

between KVN + VERA is

coming soon !!

KVN

VERA

Thank You!!

multi-frequency phase referencing vlbi observation - phase referenced image - tae hyun jung, bong...

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