Gigabit Digital Filter Bank: Digital Backend Subsystem in the VERA Data-Acquisition System
25 Feb 2005-Publications of the Astronomical Society of Japan (Oxford University Press)-Vol. 57, Iss: 1, pp 259-271
TL;DR: The Gigabit Digital Filter Bank (GDFB) as discussed by the authors was developed for the VERA project, which is a project to construct a new Japanese VLBI array dedicated to make a 3D map of our Milky Way Galaxy in terms of high precision astrometry.
Abstract: The VERA terminal is a new data-acquisition system developed for the VERA project, which is a project to construct a new Japanese VLBI array dedicated to make a 3-D map of our Milky Way Galaxy in terms of highprecision astrometry. New technology, a gigabit digital filter, was introduced in the development. The importance and advantages of a digital filter for radio astronomy have been studied as follows: (1) the digital filter can realize a variety of observation modes and maintain compatibility with different data-acquisition systems (Kiuchi et al. 1997 and Iguchi et al. 2000a), (2) the folding noise occurring in the sampling process can be reduced by combination with a higher-order sampling technique (Iguchi, Kawaguchi 2002), (3) and an ideal sharp cut-off bandedge and a flat amplitude/phase responses are approached by using a large number of taps available to use LSI of a large number of logic cells (Iguchi et al. 2000a). We developed the custom Finite Impulse Response filter chips and manufactured the Gigabit Digital Filter Banks (GDFBs) as a digital backend subsystem in the VERA terminal. In this paper, the design and development of the GDFB are presented in detail, and the performances and demonstrations of the developed GDFB are shown.
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TL;DR: In this paper, the authors used Very Long Baseline Interferometry (VLBI) observations towards the star-forming region IRAS 01123+6430 using VLBI Exploration of Radio Astrometry (VERA) to measure its annual parallax and proper motion.
Abstract: As part our investigation into the Galactic rotation curve, we carried out Very Long Baseline Interferometry (VLBI) observations towards the star-forming region IRAS 01123+6430 using VLBI Exploration of Radio Astrometry (VERA) to measure its annual parallax and proper motion. The annual parallax was measured to be 0.151+/-0.042 mas, which corresponds to a distance of D=6.61^{+2.55}_{-1.44} kpc, and the obtained proper motion components were ({\mu}_{\alpha}cos{\delta}, {\mu}_{\delta})=(-1.44+/-0.15, -0.27+/-0.16) mas yr^{-1} in equatorial coordinates. Assuming Galactic constants of (R_0, {\Theta}_0)=(8.05+/-0.45 kpc, 238+/-14 km s^{-1}), the Galactocentric distance and rotation velocity were measured to be (R, {\Theta})=(13.04+/-2.24 kpc, 239+/-22 km s^{-1}), which are consistent with a flat Galactic rotation curve. The newly estimated distance provides a more accurate bolometric luminosity of the central young stellar object, L_Bol=(3.11+/-2.86)\times 10^3 L_solar, which corresponds to a spectral type of B1-B2. The analysis of 12CO(J=1-0) survey data obtained with the Five College Radio Astronomical Observatory (FCRAO) 14 m telescope shows that the molecular cloud associated with IRAS 01123+6430 consists of arc-like and linear components, which well matches a structure predicted by numerical simulation of the cloud-cloud collision (CCC) phenomenon. The coexistence of arc-like and linear components implies that the relative velocity of initial two clouds was as slow as 3-5 km s^{-1}, which meets the expected criteria of massive star formation where the core mass is effectively increased in the presence of low relative velocity (~3-5 km s^{-1}), as suggested by Takahira et al.(2014).
1 citations
Cites methods from "Gigabit Digital Filter Bank: Digita..."
...The received signal in the observations was separated into 16 intermediate frequency (IF) channels after digital filtering (Iguchi et al. 2005), each of which had a bandwidth of 16 MHz....
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TL;DR: In this article, the authors used Very Long Baseline Interferometry (VLBI) observations towards the star-forming region IRAS 01123+6430 using VLBI Exploration of Radio Astrometry (VERA) to measure its annual parallax and proper motion.
Abstract: As part our investigation into the Galactic rotation curve, we carried out Very Long Baseline Interferometry (VLBI) observations towards the star-forming region IRAS 01123+6430 using VLBI Exploration of Radio Astrometry (VERA) to measure its annual parallax and proper motion. The annual parallax was measured to be 0.151+/-0.042 mas, which corresponds to a distance of D=6.61^{+2.55}_{-1.44} kpc, and the obtained proper motion components were ({\mu}_{\alpha}cos{\delta}, {\mu}_{\delta})=(-1.44+/-0.15, -0.27+/-0.16) mas yr^{-1} in equatorial coordinates. Assuming Galactic constants of (R_0, {\Theta}_0)=(8.05+/-0.45 kpc, 238+/-14 km s^{-1}), the Galactocentric distance and rotation velocity were measured to be (R, {\Theta})=(13.04+/-2.24 kpc, 239+/-22 km s^{-1}), which are consistent with a flat Galactic rotation curve. The newly estimated distance provides a more accurate bolometric luminosity of the central young stellar object, L_Bol=(3.11+/-2.86)\times 10^3 L_solar, which corresponds to a spectral type of B1-B2. The analysis of 12CO(J=1-0) survey data obtained with the Five College Radio Astronomical Observatory (FCRAO) 14 m telescope shows that the molecular cloud associated with IRAS 01123+6430 consists of arc-like and linear components, which well matches a structure predicted by numerical simulation of the cloud-cloud collision (CCC) phenomenon. The coexistence of arc-like and linear components implies that the relative velocity of initial two clouds was as slow as 3-5 km s^{-1}, which meets the expected criteria of massive star formation where the core mass is effectively increased in the presence of low relative velocity (~3-5 km s^{-1}), as suggested by Takahira et al.(2014).
1 citations
TL;DR: In this paper , the results of very long baseline interferometry (VLBI) observations toward an extreme OH/IR star candidate NSV 17351 are presented, which is the first report of the periodic activity of NSV17351.
Abstract: Abstract The results of astrometric very long baseline interferometry (VLBI) observations toward an extreme OH/IR star candidate NSV 17351 are presented. Using the VERA (VLBI Exploration of Radio Astrometry) VLBI array , we observed 22 GHz H2O masers of NSV 17351 and derived an annual parallax of 0.247 ± 0.035 mas, which corresponds to a distance of 4.05 ± 0.59 kpc, from the observation. By averaging proper motions of 15 maser spots further, we determined the systemic proper motion of NSV 17351 to be (μαcos δ, μδ)avg. = (−1.19 ± 0.11, 1.30 ± 0.19) mas yr−1. The maser spots spread out over a region of 20 × 30 mas, which can be converted to a spatial distribution of ∼80 × 120 au at the source distance. Internal motions of the maser spots suggest an outward-moving maser region with respect to the estimated position of the central star. From single-dish monitoring of the H2O maser emission, we estimate the pulsation period of NSV 17351 to be 1122 ± 24 d. This is the first report of the periodic activity of NSV 17351, indicating that NSV 17351 could have a mass of ∼4 M⊙. We confirmed that the time variation of H2O masers can be used as a period estimator of variable OH/IR stars. Furthermore, by inspecting dozens of double-peaked H2O maser spectra for the last 40 years, we discovered the long-term acceleration in the radial velocity of the circumstellar matter to be 0.17 ± 0.03 km s−1 yr−1. We finally determined the position and kinematics in the Milky Way Galaxy and found that NSV 17351 is located in an interarm region between the Outer and Perseus arms. We note that the astrometric VLBI observation toward extreme OH/IR stars shows us a useful sample of the Galactic dynamics.
TL;DR: Algorithms and analytical formulas aimed at predicting the induced decorrelation for a wide class of quantization schemes, with the unique assumption of weakly correlated signals, typically fulfilled in VLBI and radio astronomy applications are provided.
Dissertation•
24 Mar 2016
TL;DR: In this article, a detailed kinematics of the radio jet of 3C 84/NGC 1275 was investigated by monitoring time variability of radio jet with the VLBI Exploration of Radio Astrometry (VERA) array.
Abstract: Galaxies are fundamental elements of the universe, and consist of stars, gas, dark matterand supermassive black holes (SMBHs). It is important to understand galaxy formationand evolution when clarifying the evolution of universe. It is believed that stars aremonotonically formed from gas in galaxies, and that galaxies evolve. However, fromrecent researches on galaxy formation and evolution, it is suggested that feedback effectthat constrains star formation is a key process of galaxy evolution. One of importantfeedback effects is feedback from active galactic nucleus (AGN).AGN is a bright source at broad wavelength bands from radio to -ray in the galacticcenter. Typical size of AGN is 103 less than that of the host galaxy, but AGN shines asbrightly as the whole galaxy. This huge energy is come from gravitational energy releasedby mass accretion onto SMBH residing in the innermost region of AGN. The enormousreleased energy forms structures such as accretion disk, obscuring torus and jet in thecenter of AGN. Jets in radio-loud AGNs are relativistic plasma ow, and the size of jetis comparable to that of host galaxy, sometimes beyond host galaxy. Thus, jets play animportant role in releasing energy of host galaxy.Radio galaxies are misaligned radio-loud AGNs, and ideal sources to explore generalproperties of jets since the misalignment of the jet axis with the line of sight providesa detailed view of the structure in the jet. Radio galaxies have compact radio source,radio core, in the central region, and relatively collimated radio jets extend from radiocore. At the edge of jets, shock wave regions called hotspots are formed, and radiolobes extend beyond hotspots. Generally, these structures can be seen beyond 1,000 pcfrom the galactic center, and a big problem is how such relatively collimated and largestructures can be formed and evolved. Observationally, it is known that radio-loud AGNsmake up about 10% of the whole AGNs, and most of AGNs do not have radio jets. Thereis a problem why a part of galaxies show such phenomena. It is necessary to unveil thephysics of the vicinity of jet nozzle in order to understand the formation process of radiojet. This jet base can be spatially resolved by very long baseline interferometer (VLBI)in the radio band.Against this background, I tried to unveil the subparsec-scale radio jet of the radiogalaxy 3C 84/NGC 1275 by monitoring time variability of radio jet with the VLBI Ex-ploration of Radio Astrometry (VERA) array. Radio galaxy 3C 84 shows intermittentjet activity, and the radio brightness has increased since 2005. Thus, 3C 84 is one of thebest source to study jet properties. Using VERA, Nagai et al. (2010) found that this34activity was ascribed to the central subparsec-scale core, accompanying the ejection of anew bright component. According to the Very Long Baseline Array (VLBA) observationat 43 GHz, Suzuki et al. (2012) found that the new bright component had emerged froma radio core before 2005, and traveled southward following a parabolic trajectory on thecelestial sphere. In this study, I present the detailed kinematics of new bright componentto reveal its true nature. I investigate kinematics of new bright component in detail from2007 to 2013 by monitoring the subsequent motion for non-linear trajectory found bySuzuki et al. (2012).One of results is the apparent speed of new bright component relative to the radiocore is almost constant and sub-relativistic (0:27 0:02c) from 2007 October to 2013December. This property suggests that new bright component may be the head of mini-radio lobe including hotspots, rather than a relativistic knotty component formed asinternal shock in underlying continuous jet ow. This result implies that the radio lobein radio-loud AGNs might be already formed in subparsec-scale jets in the vicinity ofSMBHs.Another result is that new bright component might follow a helical path with a periodof about ve years thanks to highly-frequent observations. Although I cannot reliablyidentify the origin causing the wobbling motion because of the insufficient time span ofour dataset and the lack of the information of absolute reference position, the motionmight reect the accretion disk precession induced by a spinning SMBH. In order toobtain the robust result, we continue to monitor the subparsec-scale jet of 3C 84 withhigh resolution phase-referencing VLBI.As mentioned above, I found that hotspots in radio lobes in radio galaxies might bealready formed in subparsec-scale jets close to the central SMBHs. I also found thathotspots in radio lobe may be precessed by a spinning SMBH. These results are achievedby unprecedented highly-frequent observations. It is important that the fact that hotspotsmight be formed in subparsec-scale jets near the central SMBH can constrains the physicalstate such as density and velocity in jet base when understanding the formation andevolution of hotspots. Those ndings will contribute to constructing more sophisticatedtheoretical models in the future.
References
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Book•
01 Jan 1986
TL;DR: In this paper, a theory of interferometry and synthesis imaging analysis of the Interferometer Response Geometric Relationships and Polarimetry Antennas and Arrays Response of the receiving system Design of the Analog Receiving System Digital Signal Processing Very-Long-Baseline Interferometry Calibration and Fourier Transformation of Visibility Data Deconvolution, Adaptive Calibrration, and Applications Interferometers Techniques for Astrometry and Geodesy Propagation Effects Van Cittert-Zernike Theorem, Spatial Coherence, and
Abstract: Preface to the Second Edition Preface to the First Edition Introduction and Historical Review Introductory Theory of Interferometry and Synthesis Imaging Analysis of the Interferometer Response Geometric Relationships and Polarimetry Antennas and Arrays Response of the Receiving System Design of the Analog Receiving System Digital Signal Processing Very-Long-Baseline Interferometry Calibration and Fourier Transformation of Visibility Data Deconvolution, Adaptive Calibration, and Applications Interferometer Techniques for Astrometry and Geodesy Propagation Effects Van Cittert-Zernike Theorem, Spatial Coherence, and Scattering Radio Interference Related Techniques Principal Symbols Author Index Subject Index
2,025 citations
TL;DR: Using the very-long-baseline interferometer, it is found that the unresolved radio core of 3C 66B shows well-defined elliptical motions with a period of 1.05 ± 0.03 years, which provides a direct detection of a supermassive black hole binary.
Abstract: Supermassive black hole binaries may exist in the centers of active galactic nuclei such as quasars and radio galaxies, and mergers between galaxies may result in the formation of supermassive binaries during the course of galactic evolution. Using the very-long-baseline interferometer, we imaged the radio galaxy 3C 66B at radio frequencies and found that the unresolved radio core of 3C 66B shows well-defined elliptical motions with a period of 1.05 ± 0.03 years, which provides a direct detection of a supermassive black hole binary.
147 citations
Additional excerpts
...This IF configuration is available and effective in the high-precision astrometric observation toward investigating the motion and position of radio sources; e.g. the detection of the Kepler orbital motion of some emission component close to black holes (Sudou et al. 2003)....
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TL;DR: In this paper, a commercial digital oscilloscope is used as a digitizer for the 25-BEam Array Receiver System (BEARS) of the Nobeyama 45m telescope.
Abstract: New digital spectrometers for the 25-BEam Array Receiver System (BEARS) of the Nobeyama 45-m telescope are described. A commercial digital oscilloscope is used as a digitizer. The digitizer samples analogue data with 2 bits (4 levels). Data of 512 MHz bandwidth are processed for four beams at the same time. The data-formatting unit demultiplexes 2 bits 8 data in parallel to 32 parallels and sends outputs to LSIs. General purpose LSIs for autocorrelation read the digital data with a clock rate of 32 MHz. Thirty-two LSIs of 32 lags connected in cascades calculate 1024-lag autocorrelation, and output a 1024-channel power spectrum of 512 MHz bandwidth. The bandwidth of 32 MHz is achieved by picking up the data in a rate of 1/16 in the front part of the autocorrelator module. The total performances have been demonstrated by long-term integration of noise signals from receivers and observations of the Galactic star-forming region W51 in CO line.
118 citations
TL;DR: In this article, the SIS 25-BEam Array Receiver System (BEARS) is described, which is a large focal plane array receiver system for the NRO 45 m telescope.
Abstract: A large focal plane array receiver system for the NRO 45 m telescope (SIS 25-BEam Array Receiver System, or BEARS) is described. This new array receiver uses SIS junctions and has 25 elements. It can operate at the frequency range of 82 - 116 GHz. The development of this new system is almost complete. We describe about the whole system in detail, which includes the receiver, the IF systems, the new spectrometers and the remote control systems. We also describe about the performances and the uniformity of the system and show the astronomical result.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
107 citations
"Gigabit Digital Filter Bank: Digita..." refers methods in this paper
...The ADCs were fabricated by improving a digital oscilloscope made by Sony/Tektronix Company (as developed in the BEARS project: Sunada et al. 2000)....
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TL;DR: In this paper, the results of the first dual-beam observations with VERA (VLBI Exploration of Radio Astrometry) were presented, and the results demonstrate the high capability of phase referencing, indicating that it is a promising tool for phase-referencing VLBI astrometry at 10 µas-level accuracy.
Abstract: We present the results of the first dual-beam observations with VERA (VLBI Exploration of Radio Astrometry). The observations of a pair of H2O maser sources, W 49N and OH 43.8−0.1, were carried out on 2002 May 29 and July 23, and fringes of the H2O maser lines at 22GHz were successfully detected. While the residual fringe phases of both sources showed rapid variations over 360 ◦ due to the atmospheric fluctuation, the differential phase between the two sources remained constant for 1 hour with an r.m.s. of 8 ◦ , demonstrating that the atmospheric phase fluctuation was effectively removed by dual-beam phase referencing. An analysis based on the Allan standard deviation reveals that the differential phase is mostly dominated by white phase noise, and the coherence function calculated from the differential phase shows that after phase referencing the fringe visibility can be integrated for an arbitrarily long time. These results demonstrate VERA’s high capability of phase referencing, indicating that it is a promising tool for phase-referencing VLBI astrometry at 10 µas-level accuracy.
67 citations
Additional excerpts
...The results of the first dual-beam observations with our developed VERA GDFB were presented by Honma et al. (2003), demonstrating that the atmospheric phase fluctuation was effectively removed by dual-beam phase referencing....
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