坪井 昌人

We are developing the satellite (ASTRO-G) for the space VLBI mission, called VSOP-2 (Hirabayashi et al. 2004). This system will have an offset cassegrain antenna, and the three multi-mode feed horns (8, 22, 43 GHz bands) will be chosen by the Cassegrain focus position. We are designing the antenna optics of the three band receivers by using the GRASP physical optics software package on simulated feed configurations. The result of these simulations shows low cross-polarization level, a good radiation pattern, and the antenna efficiencies are 63-68 percent in these bands, assuming a perfect reflector. In this paper, we present these results of simulation of ASTRO-G antenna optics.

We present the results of multi-frequency observations of a radio flare in the young stellar object (YSO) V773 Tau, which is probably a weak-line T Tauri star. We carried out radio continuum observations at 22 GHz, 43 GHz and 86 GHz, using the Nobeyama 45 in telescope, and detected a radio flare at all frequencies. The radio flare occurred near periastron passage, and the flux density became 4 to 10 times higher, then rapidly decreased at 43 and 86 GHz within a few hours. The radio spectrum was rising (brighter at higher frequency) during the flare. On the other hand, the radio continuum at 22 GHz was detected even 28 hours later at more than 2 mJy. Thus, the active phase is surprisingly long at 22 GHz.. V773 Tau is the most promising target for detailed imaging of the magnetosphere with the next space VLBI project VSOP-2.

To achieve scientific improvements from VSOP (HALCA) to VSOP-2 (ASTRO-G), the satellite design incorporates the engineering characteristics of a large-scale deployable antenna of offset Cassegrain type with observation hands of 8, 22, and 43 GHz. The antenna subsystem requires the surface accuracy of 0.4mm RMS oil the main reflector named LDR (Large-scale Deployable Reflector) of about 9m in diameter. An off-axis paraboloid reflector is adopted to achieve this surface accuracy for millimeter-wave observation. The main reflector is composed of seven deployable modular antennas, and each of the modules employs a new idea of radial-rib/hoop-cable reflector construction to stretch metal mesh and to satisfy the required surface accuracy. The deployment mechanism employs most of the LDR technology developed for JAXA's ETS-VIII satellite, which was launched in December 2006, and both of the two antennas oil the ETS-VIII. deployed successfully on orbit. Some prototype models of one module have been made to investigate the surface accuracy. In addition, the antenna will have a two-axis adjustment mechanism for the main reflector, and a three-axis adjustment mechanism for the sub-reflector in order to optimize the antenna gain after deployment in orbit.

We are planning to construct a sub-mm VLBI system at Andes only dedicated to the detection of event horizon of SgrA*black hole. Using two of fixed large spherical dishes and a mobile small station, we sample sufficient u-v coverage, aim to image and detect the event horizon of SgrA *.

We introduce a new space VLBI project, the Second VLBI Space Observatory Program (VSOP2), following the success of the VLBI Space Observatory Program (VSOP1). VSOP2 has 10 times higher angular resolution, up to about 40 micro arcseconds, 10 times higher frequency p to 43 GHz, and 10 times higher sensitivity compared to VSOP1. Then VSOP2 should become a most powerful tool to observe innermost regions of AGN and astronomical masers. ASTRO-G is a spacecraft for VSOP2 project constructing in ISAS/JAXA Since July 2007. ASTRO-G will be launched by JAXA H-IIA rocket in fiscal year 2012. ASTRO-G and ground-based facilities are combined as VSOP2. To achieve the good observation performances, we must realize new technologies. They are large precision antenna, fast-position switching capability, new LNAs, and ultra wide-band down link, etc.. VSOP2 is a huge observation system involving ASTRO-G, ground radio telescopes, tracking stations, and correlators, one institute can not prepare a whole system of VSOP2. Then we must need close international collaboration to get sufficient quality of resultant maps and to give a sufficient quantity of observation time for astronomical community.

We performed high-resolution observations of a Galactic Center 50-km s -1 molecular cloud in the CS J = 1-0 line using the Nobeyama Millimeter Array (NMA). The molecular cloud mainly has three different spatial components with large velocity widths of up to 60kms-1. The northwest component is located at an apparent contact point to the Sgr A east shell, and elongated along the boundary of the shell. The large velocity width of the component is responsible for interaction with the Sgr A east shell. The molecular gas distribution in CS line emission is dissimilar to that observed previously in NH3 line emissions. The appearance shows presumably the area of CS line emission enhanced by shock. The central and southwest components are located just out of the Sgr A east shell and far from it, respectively. However, these components have large velocity widths. We found a well-shaped circular molecular shell with expanding motion in the 50-km s-1 molecular cloud. This is responsible for the large velocity width. The continuum source in the expanding molecular shell has a steep spectrum in mm - wavelengths, although this was not identified in a previous 5-GHz map. This source may be an SNR with an ionized sheath. From the aspect ratio of an expanding molecular shell of 1.1, the magnetic field in/around the shell is estimated to be smaller than 100μGauss. This weak magnetic field is consistent with on-going active star formation in the 50-km s-1 molecular cloud. A comparison among CS line emission, low-frequency continuum, and millimeter continuum toward the 50-km s-1 molecular cloud suggests a face-on view of the Sgr A region. The molecular cloud is located in the Sgr A halo region. © 2009. Astronomical Society of Japan.

We will introduce the observing system and operation of the ASTRO-G satellite which is the spacecraft for the VSOP-2 project that follows the success of the first space VLBI project, VSOP. VSOP-2 will have 10 times higher angular resolution (34 mu asec) and 10 times higher frequency (43 GHz), compared with VSOP, in order to observe the innermost regions of AGN jets and astronomical masers. To achieve good performance, we must obtain the 10 times higher sensitivity using new technologies. The new technologies involve a large precision antenna, fast-position switching capability, a new MMIC Low Noise Amplifiers, and a I GHz wide-band down-link. We must obtain sufficient quantity of observation time with close collaboration among ASTRO-G, ground telescopes, and tracking stations. We are forming a new international council (VISC2) to provide mission guidance on all scientific aspects related to the VSOP-2 mission..

ASTRO-G for the VSOP-2 project is a radio telescope satellite for a next-generation space very-long-baseline interferometry (VLBI) following HALCA for the VSOP project. It will be launched in 2012. We present the overview of ASTRO-G observing systems and available observing modes.

We performed the monitoring observations of the flux density toward Sgr A*, which is a compact radio source associated with a super-massive black hole located at the dynamical center of the Galaxy, using the Nobeyama Millimeter Array (NMA) and the Australia Telescope Compact Array (ATCA) at mm-wavelengths. Since 1996, the flux monitoring observations using the NMA were carried out in the 3- and 2-mm bands. Then we detected several flares of Sgr A* with typical durations of a few weeks. We also found some intraday variations (IDVs) of Sgr A* in both observing bands. The 3-mm flux observations of Sgr A* using the ATCA in the southern hemisphere were also carried out to detect IDVs with a longer observing window. In the ATCA observations, we detected IDVs of Sgr A* with timescale of a few hour. In these IDVs, the short flux-doubling timescale was estimated to be a few hours, constraining the physical size of flare-emitting region within about a few tens of AU.

The central region of our Galaxy (Sgr A*) is the nearest galactic center harboring a massive black hole. The environment around Sgr A* is a topic of interest in diverse fields. We have studied the gas feeding from giant molecular clouds (GMC) within 10 pc of the Galactic center to the Circumnuclear Ring (CND), which is presumable is infalling gas toward Sgr A*. In order to study the mechanism, we observed SiO (J=2-1 upsilon=O) and H(13)CO(+) (J=1-0) lines using the Nobeyama Millimeter Array (NMA). We detected the CND clearly in SiO line. The molecular gas in the CND rotates interactively. We observed two molecular streamers within CND in SiO line. One is a now detection. The line intensity ratios at overlapping points of the streamers in the CND are significantly higher (I(SiO)/I(H(13)CO(+)) > 8) than the average of other lines in the CND (about 2-4). This is a strong evidence indicating these streamers are associated with the CND.

Deep 1.1 mm continuum observations of 1E0657-56 (the 'Bullet Cluster') taken with the millimeter-wavelength camera AzTEC on the 10-m Atacama Submillimeter Telescope Experiment (ASTE), have revealed an extremely bright (S1.1 mm = 15.9 mJy) unresolved source. This source, MMJ065837-5557.0, lies close to a maximum in the density of underlying mass distribution, towards the larger of the two interacting clusters as traced by the weak-lensing analysis of Clowe et al. Using optical-infrared (IR) colours, we argue that MMJ065837-5557.0 lies at a redshift of z = 2.7 ± 0.2. A lensing-derived mass model for the Bullet Cluster shows a critical line (caustic) of magnification within a few arcsec of the AzTEC source, sufficient to amplify the intrinsic millimetre-wavelength flux of the AzTEC galaxy by a factor of ≫20. After subtraction of the foreground cluster emission at 1.1 mm due to the Sunyaev-Zel'dovich effect, and correcting for the magnification, the rest-frame far-IR luminosity of MMJ065837-5557.0 is ≤1012 L ⊙, characteristic of a luminous infrared galaxy (LIRG). We explore various scenarios to explain the colours, morphologies and positional offsets between the potential optical and IR counterparts, and their relationship with MMJ065837-5557.0. Until higher resolution and more sensitive (sub)millimetre observations are available, the detection of background galaxies close to the caustics of massive lensing clusters offers the only opportunity to study this intrinsically faint millimetre-galaxy population. © 2008 The Authors.

We have performed monitoring observations of the 3-millimeter flux density toward the Galactic center compact radio source Sgr A* with the Australia Telescope Compact Array (ATCA) since 2005 October. Careful calibrations of both elevation-dependent and time-dependent gains have been done to establish the variability behavior of Sgr A*. It has been found that during several observing epochs Sgr A* was quite active, showing significant intraday variation (IDV). Here we report a detected IDV event. On 2006 August 13, Sgr A* exhibits a maximum variation of 22% within 2 hrs, and two peaks with a separation of 4 hrs are seen. We discuss two possible scenarios, the orbiting hotspot model and the expanding plasmon model. © 2008 IOP Publishing Ltd.

Following the success of the first VLBI Space Observatory Programme (VSOP), a satellite of a next space VLBI project, ASTRO-G/VSOP-2, is being designed. Very Long Baseline Interferometry (VLBI) is a technique to achieve very high angular resolution imaging of celestial radio sources by combining the signals from widely separated radio telescopes. Space VLBI extends the separation beyond the Earth by placing one telescope on a satellite. The VSOP-2 satellite has an offset Cassegrain antenna. The antenna consists of a 9-m mesh-surface paraboloid main reflector, a solid hyperboloid sub-reflector, and three feed horns. The satellite has 8.0, 22, 43 GHz band receivers. The main reflector is consisting of 7 hexagonal modules. The radial rib structure is newly adopted for the modules to shape a surface with accuracy of 0.4 mm-rms. And three band feed horns are juxtaposed at the Cassegrain focus. We simulated the antenna optical performances used by physical optics method. Antenna efficiency excluding degradation by the surface accuracy are 63-68 % in all bands. Beam patterns have good symmetry and low cross-polarization level. We show the overall antenna system in this paper. © 2008 IEEE.

To achieve scientific improvements from VSOP (HALCA) mission, operated until 2005, to expected VSOP-2 (ASTRO-G) mission, the satellite design incorporates the engineering characteristics of a large-scale deployable antenna of offset Cassegrain type with observation bands of 8, 22, and 43 GHz. The antenna subsystem requires the surface accuracy of 0.4mm-rms on the main reflector named L (Large-scale Deployable Reflector) of about 9m in diameter. An off-axis paraboloid reflector is adopted to achieve this surface accuracy for millimeter-wave observation. The main reflector is composed of seven deployable modular antennas, and each of the modules employs a new idea of radial-rib/hoop-cable reflector construction to stretch knitted metal fabric surface and to satisfy the required surface accuracy. Deployment mechanism employs the most of the L technology developed for JAXA's ETS-VIII satellite. Some prototype models of one module have been made to investigate the surface accuracy. In addition, the antenna will have a gimbal adjuster mechanism for the main reflector, and a gimbals and focus adjustment mechanism for the sub-reflector in order to optimize the antenna gain after deployment in orbit.

VSOP-2 project is a next generation Space-VLBI project approved in Institute of Space and Astronautical Science (ISAS) of Japan Aerospace Exploration Agency (JAXA). The nominal launch of the VSOP-2 spacecraft, ASTRO-G, is planed in FY2012 by a HIIA rocket as the 7th astronomy satellite in ISAS/JAXA. ASTRO-G satellite will employ a 9.23-m off-axis deployable reflector antenna (LDR) with a surface accuracy of 0.4 mm rms, and cryogenically cooled receivers at 22, and 43 GHz and passively cooled receivers at 8 GHz in dual-polarization. A major axis of the orbit is 35,000 km, which will yield an angular resolution of 38 micro-arcseconds achievable at 43 GHz. Then VSOP-2 can observe innermost regions of AGN jets and astronomical masers at 10 times higher angular resolution compared to the previous Space-VLBI, VSOP(-1). These are ideal laboratories to experience physical phenomena in extreme conditions, which cannot be made in any laboratories on the earth. A phase-referencing capability of ASTRO-G satellite makes dramatic improvement of sensitivity and astrometric measurements possible. Basic design for the mechanical and thermal parts of ASTRO-G itself is on going. The radio telescope including the LDR is in EM phase. We would present the overview of VSOP-2 project.

The second space VLBI Project (VSOP-2) was approved, and just started construction of the satellite ASTRO-G in the Institute of Space and Astronautical Science (ISAS). Discussion for worldwide collaboration has also been started. Its key science targets are to investigate physical phenomena around massive black holes with, its superb spatial resolutions up to 40 micro arc seconds. By the dual, polarization, capability at all the three observing frequencies of 8, 22, and 43 GHz, VSOP-2 is anticipated, to be a powerful tool to investigate structure of accretion disk and the magnetic field structure in AGN jets to see the acceleration and collimation mechanisms. © 2008 American Institute of Physics.

We estimated synchrotron cutoff frequency of Radio Are from continuum maps at 21,45,94 GHz with the Nobeyama 45-m telescope.

We observed CO J = 1-0 and HCN J = 1-0 line emission toward a high-velocity, compact molecular cloud, CO 0.02-0.02, near the center of our Galaxy, using the Nobeyama Millimeter Array (NMA). A CO velocity-integrated map with a resolution of 4.″3 × 2.″4 shows two oval clumps with sizes of 0.8 pc. These clumps are seperated by 1.2 pc, being located at the eastern and southwestern peripheries of the CO 0.02-0.02 cloud. The overall distribution of HCN emission coincides with that taken with the Nobeyama 45 m telescope. The HCN velocity-integrated map with a resolution of 6.″ × 3.″4 shows two prominent peaks in the cloud center. Both NMA maps at VLSR ∼ 110km s-1 show an arc-shaped edge in the southeast, which may correspond to the edge of the "emission cavity" found in the CO J = 3-2 integrated-intesity map. We also noticed a faint radio continuum "arc" that encircles the bulk of the CO 0.02-0.02 cloud. These results support the notion that CO 0.02-0.02 has been accelerated, heated, and compressed in a series of supernova shocks that occurred within the last (3-5) × 104 yr. We suggest that a massive compact cluster with an age of 10-30 Myr is responsible for the formation of the CO 0.02-0.02 cloud. © 2008. Astronomical Society of Japan.

We developed a waveguide-type dual-polarization sideband-separating SIS receiver system of the 100-GHz band for the 45-m radio telescope at the Nobeyama Radio Observatory, Japan. This receiver is composed of an orthomode transducer and two sideband-separating SIS mixers, which are both based on a waveguide technique. The receiver has four intermediate frequency (IF) bands of 4.0-8.0 GHz. Over the radio frequency range of 80-120 GHz, the single-sideband receiver noise temperatures are 50-100 K, and the image rejection ratios (IRRs) are greater than 10 dB. We developed new matching optics for the telescope beam as well as new IF chains for the four IF signals. The new receiver system was installed in the telescope, and we successfully observed the 12CO, 13CO, and C18O emission lines simultaneously toward the Sagittarius B2 region to confirm the performance of the receiver system. The SSB noise temperature of the system, including the atmosphere, became approximately half of that of the previous receiver system. The IRRs of the two 2SB mixers were estimated from the 12CO and HCO+ spectra from the W 51 giant molecular cloud, resulting in > 20 dB for one polarization and > 12 dB for the other polarization. © 2008. Astronomical Society of Japan.

We present the results of multi-frequency observations of radio outbursts of the microquasar Cygnus X-3 in 2006 February and March with the Nobeyama 45-m telescope, the Nobeyama Millimeter Array, and the Yamaguchi 32-m telescope. Since the prediction of a flare by RATAN-600, the source was monitored from January 27 (UT) with these radio telescopes. At the eighteenth day after the quench of activity, successive flares exceeding 1 Jy were successfully observed. The time scale of the variability in the active phase is presumably shorter in higher frequency bands. We also present the result of a follow-up VLBI observation at 8.4 GHz with the Japanese VLBI Network 2.6 d after the first rise. A VLBI image exhibits a single core with a size of < 8 mas (80 AU). The observed image is almost stable, although the core shows a rapid variation in the flux density. No jet structure can be seen at a sensitivity of Tb (brightness temperature) = 7.5 × 105 K. © 2008. Astronomical Society of Japan.

The central region of our Galaxy (Sgr A*) is the nearest galactic center harboring a massive black bole. The environment around Sgr A* is a topic of interest to diverse fields. We are interested in gas feeding from giant molecular clouds (GMC) within 10 pc of the Galactic center to the Circumnuclear Ring (CND), which is presumable Aglay-down bayAh of infalling gas toward Sgr A*. In order to reveal the mechanism, we observed SiO J=2-1 v=O and (HCO+)-C-13 J=1-0 lines using the Nobeyama Millimeter Array (NMA). We depicted the CND clearly in SiO line. Molecular gas in CND rotates interacting each other. We observed two molecular streamers to CND in SiO line. One is a new detection. The line intensity ratios at overlapping points of streamers with CND are significantly higher (I(SiO)/I((HCO+)-C-13) > 8) than the average of CND (about 2-4). This is a strong evidence indicating these streamers are connecting to the CND.

We have performed monitoring observations of the 3-mm flux density toward the Galactic center compact radio source Sgr A* with the ATCA since 2005 October. It has been found that during several observing epochs Sgr A* was quite active, showing significant intraday variation. Here we report the detection of an IDV in Sgr A* on 2006 August 13, which exhibits a 27% fractional variation in about 2 hrs. © 2008 Copyright International Astronomical Union.

PKS 1622-297 is the most luminous gamma-ray emitting active galactic nucleus (AGN) ever detected and shows a gamma-ray intraday variability (TDV). We made a high-resolution space very long baseline interferometry (VLBI) observation of the source almost three years after the gammaray IDV. The source shows a compact core-jet structure, and all jet components have an apparent superluminal motion up to 12 h(-1) c. As an alternative probe of the sub-parsec scale structure, we also present the results from multi-epoch Australia Telescope Compact Array (ATCA) total flux monitoring, which indicate the presence of IDV. We examine the inner structure of the gamma-ray emitting AGN in light of these observations.

In 1984 an INTELSAT antenna of 32 m of diameter was constructed at 3 370 metres above the sea level on the Peruvian Andes. At the time Entel Per the Peruvian tele-communications company managed the antenna station, of almost 12 hectares in extension. In 1993 the government transferred the station to the private telecommunications company Telefnica del Per. Since transoceanic fiber optics replaced radically satellite communications in 2002, a beautiful 32- metre parabolic antenna was finished its tele-communications mission and become available for other use. So in cooperation with the National Astronomical Observatory of Japan we began coordination to transform the antenna into a radio-telescope. Researches on interstellar medium around Young Stellar Objects (YSO) are possible using methanol maser that emits at 6.7 GHz, so initially we will monitor and survey maser sources at the southern sky. An ambient temperature receiver with Trx = 60 K was developed at Nobeyama Radio Observatory and is ready to be installed. The antenna will be controlled by the Field System FS9 software installed in a PC within a Linux environment. An interface between antenna and PC was developed at Kashima Space Research Center in Japan by Mr E. Vidal. In the near future S-band (2 GHz), X-band (8GHz), 12 GHz and 22 GHz observations are planned. The peculiar position and altitude of the Peruvian Radio Observatory will be useful for VLBI observations with the VLBA for astronomical observation and geodetic measurements. For Peru where few or almost non astronomical observational instruments are available for research, implementation of the first radio observatory is a big step to foster sciences at graduate and postgraduate levels of universities. Worldwide tele-communications antennas recently tend to finish their role as tele-communications antennas. Several of them are transformed into useful observational instruments. © 2007 International Astronomical Union.

We report about the multi-frequency (1-30 GHz) daily monitoring of the radio flux variability of the three microquasars: SS433, GRS1915+105 and Cyg X-3 during the period from September 2005 to May 2006. 1. We detected clear correlation of the flaring radio fluxes and X-rays 'spikes' at 2-12 keV emission detected in RXTE ASM from GRS1915+105 during eight relatively bright (200-600 mJy) radio flares in October 2005. The 1-22 GHz spectra of these flares in maximum were optically thick at frequencies lower 2.3 GHz and optically thin at the higher frequencies. During the radio flares the spectra of the X-ray spikes become softer than those of the quiescent phase. Thus these data indicated the transitions from very high/hard states to high/soft ones during which massive ejections are probably happened. These ejections are visible as the detected radio flares. 2. After of the quiescent radio emission we have detected a drop down of the fluxes (∼20 mJy) from Cyg X-3. That is a sign of the following bright flare. Indeed such a 1 Jy-flare was detected on 3 February 2006 after 18 days of the quenched radio emission. The daily spectra of the flare in the maximum was flat from 1 to 100 GHz, using the quasi-simultaneous observations at 109 GHz with RT45m telescope and millimeter array (NMA) of Nobeyama Radio Observatory in Japan. The several bright radio flaring events (1-10 Jy) followed during this state of very variable and intensive 1-12 keV X-ray emission (∼0.5 Crab), which being monitored in RXTE ASM program. We discussed the various spectral and temporal characteristics of the detected 180-day light curves from three microquasars in comparison with Rossi XTE ASM data.

We obtained the first view in H13CO+ J = 1-0 and a high-resolution map in thermal SiO lines of G0.11-0.11, which is a molecular cloud situated between the Galactic Center radio arc and Sgr A. From a comparison with previous line observations, we found that the H 13CO+ 7 = 1-0 line is optically thin, whereas the thermal SiO lines are optically thick. The line intensity in H13CO + 7 = 1-0 shows that the cloud has a large column density, up to N(H2) = (6-7) × 1023 cm-2, which corresponds to about 640-740 mag in AV or 10-12 mag in A25 μm. The estimated column density is the largest known of any even in the Galactic center region. We conclude from the intensity ratio of SiO J = 1-0 to CS J = 1-0 that emitting gas is highly inhomogeneous for SiO abundance on a scale smaller than the beam width ∼35″. © 2006, The American Astronomical Society. All rights reserved.

A radio-IR-optical-X-ray observation campaign of SS 433 has been performed in April 2006, when the jet axis is almost perpendicular to the line of sight. Five flares have been detected during the campaign by radio monitoring observation with RATAN-600. The X-ray astronomical satellite Suzaku observed the source in and out of eclipse. In the X-ray data out of eclipse, the flux shows a significant variation with a time scale of hours. The source seems to be in the active state during the campaign. The observation logs and preliminary results are presented.

We made a high-resolution VLBI observation of the gamma-ray loud quasar PKS 1622-297 with the HALCA spacecraft and ground radio telescopes at 5 GHz in 1998 February, almost 3 yr after the source exhibited a spectacular GeV gamma-ray flare. The source shows an elongated structure toward the west on the parsec scale. The visibility data are well modeled by three distinct components: a bright core and two weaker jet components. Comparison with previous observations confirms that the jet components have an apparent superluminal motion up to 12. l h-1 c, with the inner jet components having lower superluminal speeds. We applied the inverse Compton catastrophe model and derived a Doppler factor, δ, of 2.45, which is rather lower than those of other gamma-ray loud active galactic nuclei (AGNs), suggesting that the source was in a more quiescent phase at the epoch of our observation. As an alternative probe of the subparsec-scale structure, we also present the results from multiepoch ATCA total flux monitoring, which indicate the presence of persistent intraday variability consistent with refractive interstellar scintillation. We examined the gamma-ray emission mechanism in light of these observations. © 2006. Astronomical Society of Japan.

We performed the monitoring observations of the flux density toward the Galactic center compact radio source, Sagittarius A* (Sgr A*), which is associated with a supermassive black hole, since 1996 using the Nobeyama Millimeter Array (NMA). The monitoring observations of Sgr A* were carried out in the 3- and 2-mm (100 and 140 GHz) bands over one to several months on each NMA observable season. We have detected several flares of Sgr A* with duration of, roughly, one month. The flux density at the flare peak increases 100%-200% at 100 GHz band and 200%-400% at 140 GHz band, respectively, while the averaged quiescent flux density was about 1 Jy. We also found some intraday variations (IDVs) of Sgr A* at both 2- and 3-mm bands. The shortest twofold increase timescale of the IDV is estimated to be about 1.5 hr at 140 GHz. This short timescale variability suggests that the physical size of emitting region is compact on a scale at or below about 12 AU (similar to 150 R-S). The IDV at mm-wavelengths has a similar increase timescale as those in the X-ray and infrared flares but has a smaller amplitude.

We performed high-resolution observations of the Galactic Center 50-km s(-1) molecular cloud in the CS J = 1 - 0 line using the Nobeyama Millimeter Array. The 50-km s(-1) molecular cloud corresponds to a break in the Sagittarius (Sgr) A east shell. A very broad and negative velocity wing feature is detected at an apparent contact spot between the molecular cloud and the Sgr A east shell. The velocity width of the wing feature is over 50-km s(-1). The width is three times wider than those of typical Galactic Center clouds. This strongly suggests that the shell is interacting physically with the molecular cloud. The asymmetric velocity profile of the wing feature indicates that the Sgr A east shell expands and crashes into the far side of the molecular cloud. About 50 clumps are identified in the cloud using CLUMPFIND. The velocity width-size relation and the mass spectrum of clumps in the cloud are similar to those in Central Molecular Zone (CMZ).

We obtained the detail map in H-13 CO+ and in thermal SiO lines of GO.11-0.11, which is a molecular cloud located between the Galactic Center Are and Sgr A. From line intensity ratios we found (HCO+)-C-13 line is optically thin, whereas the thermal SiO lines axe optically thick for this cloud. The cloud has a large column density up to N(H-2) = (6 - 7) x 10(23)cm(-2), which corresponds to about 640 - 740 mag in A(V) or 10 - 12 mag in A(25 mu m). This is the largest known even in the Galactic Center region. The intensity ratio of SiO to CS lines suggests that emitting gas is highly inhomogeneous for SiO abundance on a scale smaller than the beam with about 35.

It was established over a decade ago that the remarkable high-energy transients known as soft γ-ray repeaters (SGRs) are located in our Galaxy and originate from neutron stars with intense (≤ 1015G) magnetic fields-so-called 'magnetars'. On 27 December 2004, a giant flare with a fluence exceeding 0.3 erg cm-2 was detected from SGR 1806-20. Here we report the detection of a fading radio counterpart to this event. We began a monitoring programme from 0.2 to 250 GHz and obtained a high-resolution 21-cm radio spectrum that traces the intervening interstellar neutral hydrogen clouds. Analysis of the spectrum yields the first direct distance measurement of SGR 1806-20: the source is located at a distance greater than 6.4 kpc and we argue that it is nearer than 9.8 kpc. If correct, our distance estimate lowers the total energy of the explosion and relaxes the demands on theoretical models. The energetics and the rapid decay of the radio source are not compatible with the afterglow model that is usually invoked for γ-ray bursts. Instead, we suggest that the rapidly decaying radio emission arises from the debris ejected during the explosion.

We have performed the monitoring observations of the flux density of Sagittarius A* at short millimeter wavelengths (100 and 140 GHz bands) for 7 years in the period from 1996 to 2003 using the Nobeyama Millimeter Array. We found intraday variation of Sgr A* in the 2000 March flare. The flux density at the peak of the flares increases 100%-200% at 100 GHz and 200%-400% at 140 GHz (ΔS/S), respectively. The twofold increase timescale of the flare is estimated to be about 1.5 hr at 140 GHz. The intraday variation at millimeter wavelengths has a similar increase timescale as those in the X-ray and infrared flares but has smaller amplitude. This short timescale variability suggests that the physical size of the emitting region is smaller than 12 AU (≈150Rs). The decay timescale of the flare was at most 24 hr. Such a light curve with rapid increase and slow decay is similar to that often observed in outburst phenomena with ejections.

Currently a plan to convert a 32 m telecommunications antenna in the Peruvian Andes at 3,370 m above the sea level into a radio astronomy facility is in progress, it will be operated by the Institute of Geophysics in Peru (IGP) and local universities with assistance from the National Astronomical Observatory of Japan (NAOJ). In this paper we show progress on the project. © 2004 IEEE.

(1) We have three focal plane array receiver systems in the Nobeyama Radio Observatory 45-m radio telescope. These are S40M at 40 GHz, BEARS at 100 GHz, and NOB A at 150 GHz. A focal plane array receiver system at mm wavelength is superior to a single receiver system in sensitivity and also the power of reducing atmospheric effects. The telescope and these array receivers cover the wide frequency range of Rayleigh-Jeans region of the Sunyaev'-Zel'dovich (S-Z) effect. The 45-m telescope is one of most powerful tool for the observation of S-Z effect. (2) We have performed the ON-OFF observation of the S-Z effect toward eight X-ray bright galaxy clusters from z = 0.18 to 0.55 at 43 GHz using S40M as a pilot survey. The S-Z effects were detected for all clusters as temperature decrement of 0.5-1mK at the center. The Hubble constant is estimated to be H0 =64±17km/s/Mpc for a flat ACDM cosmology, which shows good agreement with the values by other S-Z effect observations. (3) The mapping observations of S-Z effect are on-going. Although most of the observed images are roughly described by the isothermal spherical β-model density distribution, the deviation from the model seems to be large for the clusters with the irregularity in the X-ray image rather than those without it. © 2004 IEEE.

The first Space-VLBI mission, VSOP, started successfully with the launch of the dedicated space-VLBI satellite HALCA in 1997. The mission has been in scientific operation in the 1.6 GHz and 5 GHz bands, and studies have been done mainly of the jet phenomena related to active galactic nuclei. Observing at higher frequencies has the advantage of less absorption through the ambient plasma and less contribution from scattering, and also has the merit of resulting in higher angular resolution observations. A second generation space-VLBI mission, VSOP-2, has been planned by the working group formed at ISAS/JAXA with many collaborators. The spacecraft is planned to observe in the 8, 22 and 43 GHz bands with cooled receivers for the two higher bands, and with a maximum angular resolution at 43 GHz (7 mm) of about 40 micro-arcseconds. The system design, including the spacecraft and ground facilities, will be introduced, and the impact for sub-mm space-VLBI further into the future will be discussed.

We have observed circular polarization of Sgr A* at 100 GHz using the Nobeyama 45-m telescope. The circular polarization of Sgr A* in its quiescent phase was |mc| ≤ 0.5% after subtraction of the contribution from free-free emission surrounding Sgr A*. © 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The CS observations with NRO 45m telescope reveal that a dense molecular shell is located between Sgr A and the nonthermal filaments of the radio arc, and that the shell shows an interacting feature with the nonthermal filaments (Tsuboi et al. 1997). The shell is associated with X-ray emission observed with ASCA and Chandra (Yusef-Zadah et al. 2002). These result suggests the shell is formed by a shock.The SiO lines in the v = 0 state are thermally excited and are thought to be a shock tracer. They are good probes to investigate the physical property of the shell. We observed the shell in SiO (J = 1 - 0, v = 0) and SiO (J = 2 - 1, v = 0) using the NRO 45m telescope.Features associated with the shell clearly appear in both the SiO lines. The morphology of the shell in both SiO lines after adjusting the beamsize effect is similar in l - b - v 3-dimensional space. The intensity ratio of the two SiO lines (J = 2 - 1 over J = 1 - 0) is uniform over the shell, suggesting the shell is uniform in density. We estimate the average value of the ratio R2-1/1-0 approximate to 0.9, which means the molecular gas density is about 10(5) cm(-3) using multi-level population analysis with the LVG approximation.The morphology of the shell in SiO lines is quite similar to in the CS line in l - b - v 3-dimensional space. The intensity ratio of SiO (J = 1 - 0) to CS (J = 1 - 0) is almost uniform over the shell and R-SiO/CS approximate to 0.24. The ratio of the SiO (J = 1 - 0) line over the CS (J = 1 - 0) line is about 0.24, which means the relative abundance of SiO over CS, X(SiO)/X(CS) approximate to 0.05 - 0.13 using multi-level population analysis with the LVG approximation. It is close to the value found in an SNR shell.

We have performed intensity monitoring observations toward the Galactic center compact non-thermal radio source, Sagittarius A*, at lambda= 3 and 2 mm (100 and 140 GHz) from 1996 to 2002 using the Nobeyama Millimeter Array (NMA). In 1996, 1997, 1998, and 2000, the observations were performed during a period of one to two months for each year in a single (intermediate resolution) array configuration in order to exclude a systematic error caused by sampling different source structures with the different beam sizes. From November 2000 to May 2001, and from November 2001 to May 2002, the observations were carried out over several months in order to investigate the longer term variability. We have detected two flares in March 2000 and April 2002 as well as a flare observed in March 1998 (Tsuboi et al. 1999). The peak flux densities of the flares were 2-3 Jy at 3 mm, while the mean quiescent flux densities was similar to 1 Jy. In particular for the March 2000 flare, the flux densities of Sgr A* at 2 mm had also reached a peak, similar to 4 Jy, on 8 March and increased Delta S/S similar to 300%. The flux density decreased by half in a day. We have detected the intra-day variability of Sgr A*. The upper limit for size of the variable component estimated from timescale of the flare is a few tens of AU. For spectra made from our observations at mm-wavelengths, the variability of flux density increases with frequency. It appears that the variability in the flare propagates from higher to lower frequency. The folded lightcurve with 106 days cycle, which determined from the analysis of the VLA cm-wavelength data, shows distinct high and low activity states. These results provide evidence for quasiperiodic variability of the flux density of Sgr A* at mm-wavelengths.

We have observed the Sunyaev-Zel'dovich (S-Z) effect towards four distant galaxy clusters from z = 0.18 - 0.55 at 43 GHz using a newly developed 6-beam receiver installed in the Nobeyama 45-m telescope. The S-Z effects at the cluster center at the Rayleigh-Jeans limit are -1.38 +/- 0.07 mK for CL0016+16, -0.95 +/- 0.20 mK for MS1358+62, -0.63 +/- 0.16 mK for MS1008-12, and -0.73 +/- 0.10 mK for A2218, respectively. The S-Z effect for MS1008-12 is a new detection. Assuming that the dimensionless cosmological constant is Omega(Lambda) = 0.7, the Hubble constant is estimated to be H-0 = 67 +/- 13 krn s(-1) Mpc(-1). This is consistent with the value in the nearby universe obtained by the Hubble Space Telescope (HST). On the contrary, assuming that the derived value is equal to that by HST, the results are in agreement with the dimensionless cosmological constant Of Omega(Lambda) similar to 0.7.

We have designed and constructed a tunable polarimeter system to cover frequencies from 35 GHz to 250 GHz, (8.6 mm and 1.2 mm in wavelength) for the 45m telescope at Nobeyama Radio Observatory (NRO). Both circular and linear polarizations can be measured by the polarimeter. The performance of the polarimeter in astronomical observations was tested by simultaneously measuring the linear polarization of the J = 2 - 1 transition of SiO in the nu=0 and 1 states at 86 GHz toward VY CMa. The design, construction, and tests are presented briefly.

We briefly report the results of polarimetric observations of SiO emission from late-type stars taken with a millimeter polarimeter installed at the Nobeyama 45m telescope. We found that the SiO J = 2 - 1 emission in the v = 0 state from R Cas contains a highly linearly polarized component, followed by the detection of highly linearly polarized emission of the same transition from VY CMa (Shinnaga et al. 1999). The high polarization degree is a strong evidence that the v=0 emission originates from maser action. We found out that, not only a peculiar supergiant star, but also a Mira variable star is associated with the SiO v = 0 maser.

Large-scale CO images taken with the 2 × 2 focal-plane array receiver on the 45 m telescope of Nobeyama Radio Observatory reveal parsec-scale structure of molecular gas around the Galactic center radio arc. The LVG analysis shows that the gas kinetic temperature is considerably enhanced (Tk ≥ 70K) in CO 0.13-0.13, a cloud which seems to be in contact with the nonthermal filaments of the Galactic center radio arc. This lends support for an interaction between CO 0.13-0.13 and the nonthermal filaments. The interaction with the strong magnetic field in and around the nonthermal filaments may heat up the molecular gas in CO 0.13-0.13 through shock dissipation and/or magnetic viscosity. We also find an expanding cavity adjacent to the nonthermal filaments. The shell has a radius of ∼ 5 pc and an expansion velocity of 25kms-1. This expanding cavity might have been formed by several hundred supernovae or a single hypernova within 3 × 105 yr. Magnetic tubes in this region could have been swept up by the expanding cavity, and compressed by interactions with CO 0.13-0.13. An interaction between the cloud and magnetic field may accelerate electrons to relativistic energies through shock acceleration or magnetic field reconnection.

We report on the detection of a high-velocity feature, CO 1.27+0.01, in the Galactic-center molecular-cloud complex. In our 12CO images taken with the NRO 45m telescope, CO 1.27+0.01 appears as the second prominent high-velocity feature, next to CO 0.02-0.02, having a velocity width of Δ V ≃ 100kms-1 and a size of 9pc × 12pc. It seems to consist of two expanding shells with sizes of ∼ 10 pc. The major shell has a kinetic energy of about an order of magnitude larger than the gravitational energy, indicating that the shell is apparently gravitationally unbound. We propose that CO 1.27+0.01 may have been accelerated by a series of supernova explosions which occurred within the last ∼ 6 × 104 yr. No association of a nonthermal radio continuum source suggests a strong magnetic field (B ≳ 0.4mG) in the vicinity of CO 1.27+0.01.

We have made a wide-field survey of SiO masers in the 7′ × 13′ area around the Galactic center with the Nobeyama 45-m radio telescope using a 2 × 3 multi-beam SIS mixer receiver at 43 GHz. We detected 9 SiO maser sources (6 of them are new); newly detected 6 sources have not been identified with Miras or OH 1612 MHz maser sources. The source surface number density, ∼ 360 per square degree, found in this survey is slightly smaller than the number density of OH 1612 MHz sources in the same area. A least-squares analysis of the radial velocities of the detected sources has revealed a rapid rotation of the stars around the Galactic center. This implies that most of the objects detected in this survey belong to the nuclear disk near the Galactic center.

We have observed three molecular clumps in the Galactic center region in the CS J=2-1 line with the Nobeyama Millimeter Array. We have determined the mass spectrum and other statistical relations for the Galactic center cloud cores. The derived mass spectrum is somewhat steeper than for galactic cloud cores based on molecular line observations. In addition, the spectrum is steeper than that of the large scale Galactic center clumps.