Mamoru Sekido

Ultra-rapid UT1 measurement by e-VLBI

The latency of UT1 measurement with Very Long Baseline Interferometry (VLBI) has been greatly reduced by using e-VLBI technology. VLBI observations on the baseline formed by the Kashima 34-m and the Onsala 20-m radio telescopes achieved ultra-rapid UT1 measurements, where the UT1 result was obtained within 30 min after the end of the observing session. A high speed network and a UDP-based data transfer protocol ‘Tsunami’ assisted the high data rate and long-distance data transfer from Onsala to Kashima. The accuracy of the UT1 value obtained from the 1-h single baseline e-VLBI experiment has been confirmed to be as the same level with the rapid combined solution of Bulletin-A. The newly developed technology is going to be transferred to the regular intensive VLBI sessions, and it is expected to contribute to the improved latency and accuracy of UT1 data.

VLBI observation of narrow bandwidth signals from the spacecraft

We carried out a series of VLBI observations of Nozomi by using a dedicated narrow bandwidth VLBI system. The three carrier waves with frequency interval of 515 kHz were recorded in 3 channels of the system and correlated by a software method. As a result of the correlation, the residual fringe phases of the main carrier wave are obtained for every 1.3 seconds. We can also continuously track them for 100 minutes. The variation of the residual fringe phase is +/− 150 degrees. Moreover, we can derive succesively the group delay for every 100 seconds by using these three carrier waves. The RMS of the group delays is 13 nsec and its average is well accorded with the delay determined by the range and Doppler measurements within an error of 2 nsec. Consequently, we confirmed the validity of the narrow bandwidth VLBI system, and it could be expected that this system, in addition to range and Doppler measurements, can be applied to three-dimensional tracking of a spacecraft and the precise gravity measurement of the Moon and the planets.

Automated geodetic Very Long Baseline Interferometry observation and data analysis system

A precise geodetic measurement network using three modern space geodetic techniques, i.e. Very Long Baseline Interferometry, Satellite Laser Ranging, and Global Positioning System, is being established around Tokyo, Japan by the Communications Research Laboratory. The Key Stone Project, which is the name of the project, was started to obtain precise relative positions of four stations using these three space geodetic techniques on a daily basis. The system was designed to make frequent observations possible with minimum human operations and to provide analyzed results as fast as possible. This paper describes various aspects of new features and the performance of the automatic geodetic Very Long Baseline Interferometry observation and data analysis system designed for the Key Stone Project. This automated design has allowed daily Very Long Baseline Interferometry experiments to be conducted since January 1995 and the results to be immediately made available for public use after each experiment.

J-Net Galactic-Plane Survey of VLBI Radio Sources for VLBI Exploration of Radio Astrometry (VERA)

In order to search for new VLBI sources in the Galactic plane that can be used as phase reference sources in differential VLBI, we have conducted 22 GHz observations of radio sources in the Galactic plane using the Japanese VLBI Network (J-Net). We have observed 267 VLBI source candidates selected from existing radio surveys and have detected 93 sources at the signal-to-noise ratio larger than 5. While 42 of the 93 detected sources had already been detected with VLBI at relatively lower frequency (typically 2 to 8 GHz), the remaining 51 are found to be new VLBI sources detected for the first time. These VLBI sources are located within

VLBI Detections of Parsec-Scale Nonthermal Jets in Radio-Loud Broad Absorption Line Quasars

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Multifrequency Study of Giant Radio Pulses from the Crab Pulsar with the K5 VLBI Recording Terminal

, and have a large number of Galactic maser sources around them. Thus, they are potential candidates for phase reference sources for VLBI Exploration of Radio Astrometry (VERA), which is the first VLBI array dedicated to the phase referencing VLBI astrometry aiming at measuring the parallax and proper motion of maser sources in the whole Galaxy.

Optical grid infrastructure: Establishing multiple end-to-end lightpaths in optical networks

We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey (SDSS) Third Data Release, by a very-long-baseline interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network (JVN). We aimed at selecting BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversial issues of whether BAL quasars are viewed nearly edge-on, and of whether BAL quasars are in a short-lived evolutionary phase of quasar population. We detected 20 out of 22 sources using the OCTAVE baselines, implying brightness temperatures greater than 10^5 K, which presumably come from nonthermal jets. Hence, BAL outflows and nonthermal jets can be generated simultaneously in these central engines. We also found four inverted-spectrum sources, which are interpreted as Doppler-beamed, pole-on-viewed relativistic jet sources or young radio sources: single edge-on geometry cannot describe all BAL quasars. We discuss the implications of the OCTAVE observations for investigations for the orientation and evolutionary stage of BAL quasars.

Evaluation of repeatability of baseline lengths in the VLBI network around the Tokyo metropolitan area

AbstractSimultaneous multifrequency observations of the Crab pulsar giant pulses (GPs)were performed with the 64-m Kalyazin radio telescope at four frequencies ν = 0.6,1.4, 2.2 and 8.3 GHz, using the K5 VLBI recording terminal. The K5 terminal pro-vided continuous recording in 16 4-MHz wide frequency channels distributed over 4frequency bands. Several thousand GPs were detected during about 6 hours of obser-vations in two successive days in July 2005. Radio spectra of single GPs were analysedat separate frequencies and over the whole frequency range. These spectra mani-fest notable modulation over frequency ranges, ∆ν, both on large (∆ν/ν ≈ 0.5) andsmall (∆ν/ν ≈ 0.01) frequency scales. Cross-correlation analysis of GPs at 2.2 GHzshowed that their pulse shapes can be interpreted as an ensemble of unresolved burstsgrouped together at time scales of ≈1 µs being well-correlated over a 60-MHz band.The corresponding GP cross-correlation functions do not obey the predictions of theamplitude-modulated noise model of Rickett (1975), thus indicating that unresolvedcomponents represent a small number of elementary emitters.Key words: Pulsars — giant pulses, Crab pulsar, PSR B0531+21 — e-VLBI1

Effective expansion of satellite laser ranging network to improve global geodetic parameters

We introduce our optical grid infrastructure where end-to-end, bandwidth-guaranteed lightpaths are established simultaneously. This is developed on a lightpath network that employs wavelength-routing. One application may send a request for multiple lightpaths to the network, which establishes the lightpaths one-by-one. Thus, several lightpaths may be rejected due to simultaneous reservation of an identical wavelength or undesired wavelength use. The proposed control-layered structure consisting of application, optical-grid control, and optical-network control layers bridges the gap between applications and optical networks. The optical-grid control layer translates an application request to form a set of lightpaths into multiple requests for the network. This layer is also capable of adjusting the available network interfaces of the hosts and the available wavelengths of the network such that all the lightpaths are likely to be established. We address our testbed network in the Tokyo metropolitan area and a collaborative work with e-VLBI (Very Long Baseline Interferometry), which requires long-distance, high-speed, and non-data loss communication circuits in the network.

NO MICROWAVE FLARE OF SAGITTARIUS A* AROUND THE G2 PERIASTRON PASSING

Since 1995, VLBI measurements using fixed VLBI stations around the Tokyo metropolitan area have been continually producing data of station positions and baseline lengths. The accuracy of baseline length measurements is evaluated in terms of repeatability, conventionally defined as a standard deviation of those obtained by five continuous sessions. Continuous improvement both in system hardware and in the observation method have resulted in a remarkable improvement in measurement accuracy. Repeatability reaches about a 2-mm level in baseline length in our VLBI network.