Kazuhiro Takefuji

High-order Sampling Techniques of Aliased Signals for Very Long Baseline Interferometry

Radio frequency (RF) direct sampling is a technique used to sample RF signals that are higher than the sampling rate, without the use of a frequency converter and an anti-aliasing filter. In the case of geodetic VLBI, the RF frequency is at most 9 GHz. Recently, a digital sampler with high sensitivity at RF frequencies greater than 10 GHz was developed. The sampler enables us to evaluate the use of the RF direct sampling technique in geodetic VLBI. RF direct sampling has the potential to make the system simple and stable because, unlike a conventional system, analog frequency converters are not used. We have developed two sets of RF direct sampling systems and operated them on Kashima and Tsukuba baseline (about 50 km length) in Japan. At first, we carried out the VLBI experiment only for X band (8 GHz) signals and successfully got the first fringes. Aliased signals could be discriminated through correlation processing. Then, we adopted RF direct sampling for mixed signals, i.e., S band (2 GHz) and X band signals are combined with each other to make a geodetic VLBI observation. We carried out a 24 hr geodetic VLBI session on 2011 October 19 and succeeded in fringe detection for both S and X bands. After correlation processing, baseline analysis was carried out and we got results consistent with those obtained by conventional VLBI.

Very Long Baseline Interferometry Experiment on Giant Radio Pulses of Crab Pulsar toward Fast Radio Burst Detection

We report on a very long baseline interferometry (VLBI) experiment on giant radio pulses (GPs) from the Crab pulsar in the radio 1.4 to 1.7 GHz range to demonstrate a VLBI technique for searching for fast radio bursts (FRBs). We carried out the experiment on 26 July 2014 using the Kashima 34 m and Usuda 64 m radio telescopes of the Japanese VLBI Network (JVN) with a baseline of about 200 km. During the approximately 1 h observation, we could detect 35 GPs by high-time-resolution VLBI. Moreover, we determined the dispersion measure (DM) to be 56.7585 +/- 0.0025 on the basis of the mean DM of the 35 GPs detected by VLBI. We confirmed that the sensitivity of a detection of GPs using our technique is superior to that of a single-dish mode detection using the same telescope.

Development of cross-correlation spectrometry and the coherent structures of maser sources

We have developed a new method of data processing for radio telescope observation data to measure time-dependent temporal coherence, and we named it cross-correlation spectrometry (XCS). XCS is an autocorrelation procedure that expands time lags over the integration time and is applied to data obtained from a single-dish observation. The temporal coherence property of received signals is enhanced by XCS. We tested the XCS technique using the data of strong H2O masers in W3 (H2O), W49N and W75N. We obtained the temporal coherent lengths of the maser emission to be 17.95

Development of wideband VLBI system with transportable small telescope for distant frequency transfer

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Method for Finding Variable Radio Sources in Drift-Scan Interferometric Data from the Nasu Observatory

0.33 {\mu}s, 26.89

Development of the Phase-up Technology of the Radio Telescopes: 6.7 GHz Methanol Maser Observations with Phased Hitachi 32 m and Takahagi 32 m Radio Telescopes

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An algorithm of wideband bandwidth synthesis for geodetic VLBI: WIDEBAND BANDWIDTH SYNTHESIS

0.49 {\mu}s and 15.95

Caravan-Submm, Black Hole Imager in the Andes

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Sear ch for a correlation between giant radio pulses and hard X-ray emissions in the Crab pulsar

0.46 {\mu}s for W3 (H2O), W49N and W75N, respectively. These results may indicate the existence of a coherent astrophysical maser.

e-VLBI Activities in Japan

Very long baseline interferometry (VLBI) is one of the technologies to enable comparisons of atomic frequency standards at intercontinental baseline. Our group is working on development of wideband VLBI system with transportable small diameter antennas for VLBI application to the frequency transfer. The system is composed of pair of small diameter antennas and large diameter antenna, which observes ultra-wide frequency range at 3-14GHz. This paper reports the overview of the project and current status of the development.