1 gbps disk-based vlbi observation for future east asia vlbi observations kiyoaki wajima 18 march...

1 Gbps Disk-Based VLBI Observation for Future East Asia VLBI Observations

Kiyoaki Wajima

18 March 2009 동아시아 VLBI 워크샵

Yamaguchi University

Introduction

Observation and Results

Future Observation Plan

Summary

Contents

Observation by K5/VSI with delight

I. Introduction

Wideband Observation in VLBI• Minimum sensitivity for a continuum source in VLBI

　　　　　　　　　　⇒ Smin ∝ B-1/2

– Expansion of bandwidth with high-speed sampling and data recording for better sensitivity

• Conventional VLBI recording system has a dedicated recorder with a magnetic tape drive


General-purpose instrument by commercial PC specification having VLBI data recording and correlation function

K5/VSI System• Disk-based VLBI recording system developed by NICT• VLBI Standard Interface (VSI)-compliant data

recording with a data rate of 1 Gbps or higher– System configuration at low cost compared to dedicated

recording system

– Software correlation capability

K5/VSI recorder (lower) and VSI-H compliant sampler ADS-1000 (upper)

(image courtesy of NICT)

We made test observations using K5/VSI for future EAVN observations


II. Observation and Results

Test Observation Summary• Test Observations with K5/VSI

– Date: 26, 27 June 2008

– Station: Yamaguchi 32 m, Kashima 34 m(baseline length: 850 km = 30 Mλ)

– Frequency: 8 GHz

– Target: 3C 273

– Observation made with three sampling modes (512 MHz bandwidth each)

• 1 Gsps, 1-bit sampling at each station

• 2 Gsps, 2-bit sampling at each station

• Mixed recording with 1-bit (Yamaguchi) and 2-bit (Kashima)

• Integration time: 1 ~ 10 seconds


Kashima 34 m Telescope

Yamaguchi 32 m Telescope

We are here!

Results• Fringes were successfully detected in 27 June

observation for all sampling modes

Example of fringe search results. 1-bit quantization, 1 Gbps recording, and integration time of 3 seconds


Results (cont’d)• Expected fringe SNR

– 1-bit sampling, B = 512 MHz, τ = 1 sec, Tsys ~ 50 K (Yamaguchi) , ~ 80 K (Kashima), Sν ~ 8 Jy (~ 30 Mλ)

MOJAVE 15 GHz visibility plot for 3C273 on 17 July 2008

VLBA calibrator survey 8 GHz visibility plot for 3C273 on 14 July 2004

Q e1 e2SN

B sys1 sys2

2 5502

S A AR B

k T T Consistent with our

observation results


Results (cont’d)• Effects of integration time and

quantization for fringe SNR– Effect of integration time (upper)

SNR ∝ t1/2

– Sensitivity relative to the nonquantizing case

• 1-bit (2-level): 64%

• 2-bit (4-level): 88%

• 1/2-bit mixed correlation: 75%

→ sensitivity relative to the 1-bit quantization (lower)

• 1/2-bit mixed correlation: 117%

• 2-bit (4-level): 138%


Results (cont’d)• Effects of integration time for fringe SNR

Calculated and observed fringe SNR for each integration time relative to SNR for the integration time of 1 second in the same sampling mode


Results (cont’d)• Quantization effects for fringe SNR

Calculated and observed fringe SNR for each sampling mode relative to SNR for the 1-bit sampling in the same integration time


Results (cont’d)• 27 June 2009 results (summary)

Sampling mode Int. time[sec]

SNR SNR ratio(int. time)

SNR ratio(quantization effect)

1-bit 1 439.3 －－1-bit 3 737.2 1.68 －1-bit 5 979.8 2.23 －

1/2-bit mixed 1 481.7 － 1.101/2-bit mixed 3 888.9 1.85 1.211/2-bit mixed 5 1042.4 2.16 1.06

2-bit 1 605.6 － 1.382-bit 3 1054.1 1.74 1.432-bit 5 1397.3 2.31 1.43

The results of each fringe SNR are consistent with theoretical values in terms of the integration time and quantization effects.


III. Future Observation Plan

EAVN Observations with K5/VSI• Sampler with VSI-compliant output format (we

suppose the ADS-1000 sampler) ⇒ VLBI observations with K5/VSI– Test observations and initial

scientific results with KVN-internal baselines

– International VLBI experiments with K5/VSI for EAVN

KVN digital data acquisition system


Future Test Observation• 22/43 GHz receiver installation at KVN Seoul and

Ulsan station by June 2009 (Han-san’s talk)– Test observations with VERA and JVN in 2009

– K4/VSOP terminal with 256 Mbps (Miyazaki-san’s talk)

• Current development at Yamaguchi University– 22 GHz cooled receiver system installation at Yamaguchi

station

– New K5/VSI instruments (my talk)

Test experiments and scientific observations between Korea and Japan


Observation of Young Radio Galaxy


• Spectral age, tsyn, of young radio galaxies(CSO, GPS, HFP)

Exploring the physicalevolution of radio galaxies

Multifrequency, widebandradio spectra for the lobes

(νbr : Synchrotron break frequency)

1.5 0.5

4 brsyn 5.02 10 [yr]

[mG] [GHz]

Bt

(Nagai et al. 2006, ApJ, 648, 148)

br

IV. Summary

Summary

We made VLBI observations with K5/VSI at 8 GHz and fringes were successfully detected. The results of each fringe SNR are consistent with theoretical values in terms of the integration time and quantization effects. On the basis of test observation results, we are planning to carry out test experiments and

to obtain scientific results.18 March 2009 동아시아 VLBI

워크샵

为了东亚 VLBI…동아시아 VLBI 를

위하여…

Thank you for your kind attention.どうもありがとうございました

1 gbps disk-based vlbi observation for future east asia vlbi observations kiyoaki wajima 18 march...

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