坪井 昌人

We built a Ka-band dual-circular-polarization low-noise receiver for the Misasa 54 m parabola antenna in Misasa, Japan. The antenna is designed to be combined with a transmitter and receiver system at the X band (around 8 GHz) and simultaneously with a receiver system at the Ka band. The Ka band is the frequency band around 30 GHz, which is important for deep-space communications and radio astronomy. The receiver comprises some waveguide components including a feed horn, a circular polarizer, and low-noise amplifiers. The components are installed in a vacuum vessel and are cooled to 4 K with a Gifford-McMahon refrigerator, providing low-noise performance. The receiver is capable of simultaneously handling the left- and right-hand circular-polarization (LHCP and RHCP) channels. The receiver-noise temperature was measured to be T-RX similar or equal to 14 K in both the LHCP and RHCP channels. The system-noise temperature, including the antenna loss and atmospheric attenuation at the zenith, was measured to be T-sys = 36-37 K in both the LHCP and RHCP channels on a clear day in September at Misasa. When the receiver is used with the X-band transmitter, the system-noise temperature is maintained at T-sys similar or equal to 42 K in the RHCP channel. The degradation in the system-noise temperature is attributed to a frequency-selective reflector, which divides the signals in the X and Ka bands. There is no contamination from the transmitter to damage the receiver. The receiver has already been in use for deep-space communications and radio-astronomy observations. Our team in the radio-astronomy laboratory of ISAS/JAXA is responsible for the development of the receiver and the measurements of its performance.

We present the results based on the 2.5 arcsec-resolution observations using Atacama Large Millimeter/submillimeter Array (ALMA) of the Galactic Center Molecular Cloud G-0.02-0.07, or the 50 km/s Molecular Cloud (50MC), in the SO (N_J=2_2-1_1) line and 86-GHz continuum emission, the combination of which is considered to trace "hot molecular core candidates" (HMCCs) appearing in the early stage of massive star formation. In the 86-GHz continuum image, we identified nine dust cores in the central part of the 50MC, in which four famous compact HII regions are located. No new ultra-compact HII regions were found. We also identified 28 HMCCs in the 50MC with the SO line. The overall SO distribution had no clear positional correlation with the identified HII regions. The HMCCs in the 50MC showed a variety of association and non-association with dust and Class-I CH3OH maser emissions. The variety suggests that they are not in a single evolutionary stage or environment. Nevertheless, the masses of the identified HMCCs were found to be well approximated by a single power law of their radii, M_LTE/(M_sun)=5.44 x 10^5 (r/(pc))^2.17 at T_ex = 50-100 K. The derived HMCC masses were larger than those of the molecular cores with the same radii in the 50MC and also than those of the molecular clumps in the Galactic disk. Additional observations are needed to confirm the nature of these HMCCs in the 50MC.

<title>Abstract</title> We performed a search of cloud–cloud collision (CCC) sites in the Sagittarius A molecular cloud (SgrAMC) based on the survey observations using the Nobeyama 45 m telescope in the C32S J = 1–0 and SiO v = 0 J = 2–1 emission lines. We found candidates abundant in shocked molecular gas in the Galactic Center Arc (GCA). One of them, M0.014−0.054, is located in the mapping area of our previous ALMA mosaic observation. We explored the structure and kinematics of M0.014−0.054 in the C32S J = 2–1, C34S J = 2–1, SiO v = 0 J = 2–1, H13CO+J = 1–0, and SO N, J = 2, 2–1, 1 emission lines and fainter emission lines. M0.014−0.054 is likely formed by the CCC between the vertical molecular filaments (the “vertical part,” or VP) of the GCA, and other molecular filaments along Galactic longitude. The bridging features between these colliding filaments on the PV diagram are found, which are the characteristics expected in CCC sites. We also found continuum compact objects in M0.014−0.054, which have no counterpart in the H42α recombination line. They are detected in the SO emission line, and would be “hot molecular cores” (HMCs). Because the local thermodynamic equilibrium mass of one HMC is larger than the virial mass, it is bound gravitationally. This is also detected in the CCS emission line. The embedded star would be too young to ionize the surrounding molecular cloud. The VP is traced by a poloidal magnetic field. Because the strength of the magnetic field is estimated to be ∼mgauss using the Chandrasekhar–Fermi method, the VP is supported against fragmentation. The star formation in the HMC of M0.014−0.054 is likely induced by the CCC between the stable filaments, which may be a common mechanism in the SgrAMC.

The Galactic Center IRS 13E cluster is a very intriguing IR object located at $\sim0.13$ pc from Sagittarius A$^\ast$ (Sgr A$^\ast$) in projection distance. There are both arguments for and against the hypothesis that a dark mass like an intermediate mass black hole (IMBH) exists in the cluster. Recently we have detected the rotating ionized gas ring around IRS 13E3, which belongs to the cluster, in the H30$\alpha$ recombination line using ALMA. The enclosed mass is derived to be $M_{\mathrm{encl. } }\simeq2\times10^4$ $M_\odot$, which agrees with an IMBH and is barely less than the astrometric upper limit mass of the IMBH around Sgr A$^\ast$. Because the limit mass depends on the true three-deminsional (3D) distance from Sgr A$^\ast$, it is very important to determine it observationally. However, the 3D distance is indefinite because it is hard to determine the line-of-sight (LOS) distance by usual methods. We would attempt to estimate the LOS distance by spectroscopic informations. The CH$_3$OH molecule is easily destroyed by cosmic ray around Sgr A$^{\ast}$. However, we detected a highly excited CH$_3$OH emission line in the ionized gas stream associated with IRS 13E3. This indicates that IRS 13E3 is located at $r\gtrsim 0.4$ pc from Sgr A$^{\ast}$.

<title>Abstract</title> We have observed the compact H ii region complex nearest to the dynamical center of the Galaxy, G−0.02−0.07, using ALMA in the H42α recombination line, CS J = 2–1, H13CO+J = 1–0, and SiO v = 0, J = 2–1 emission lines, and the 86 GHz continuum emission. The H ii regions HII-A to HII-C in the cluster are clearly resolved into a shell-like feature with a bright half and a dark half in the recombination line and continuum emission. The analysis of the absorption features in the molecular emission lines show that H ii-A, B, and C are located on the near side of the “Galactic center 50 km s−1 molecular cloud” (50MC), but HII-D is located on the far side of it. The electron temperatures and densities ranges are Te = 5150–5920 K and ne = 950–2340 cm−3, respectively. The electron temperatures in the bright half are slightly lower than those in the dark half, while the electron densities in the bright half are slightly higher than those in the dark half. The H ii regions are embedded in the ambient molecular gas. There are some molecular gas components compressed by a C-type shock wave around the H ii regions. From the line width of the H42α recombination line, the expansion velocities of HII-A, HII-B, HII-C, and HII-D are estimated to be Vexp = 16.7, 11.6, 11.1, and 12.1 km s−1, respectively. The expansion timescales of HII-A, HII-B, HII-C, and HII-D are estimated to be tage ≃ 1.4 × 104, 1.7 × 104, 2.0 × 104, and 0.7 × 104 yr, respectively. The spectral types of the central stars from HII-A to HII-D are estimated to be O8V, O9.5V, O9V, and B0V, respectively. These derived spectral types are roughly consistent with the previous radio estimation. The positional relation among the H ii regions, the SiO molecule enhancement area, and Class-I maser spots suggest that a shock wave caused by a cloud–cloud collision propagated along the line from HII-C to HII-A in the 50MC. The shock wave would have triggered the massive star formation.

© 2019 The Author(s). Published by Oxford University Press on behalf of the Astronomical Society of Japan. We detected a compact ionized gas associated physically with IRS13E3, an intermediate mass black hole (IMBH) candidate in the Galactic center, in the continuum emission at 232 GHz and H30α recombination line using ALMA Cy.5 observation (2017.1.00503.S, P.I. M.Tsuboi). The continuum emission image shows that IRS13E3 is surrounded by an oval-like structure. The angular size is 0′′.093 ± 0′′.006 × 0′′.061 ± 0′′.004 (1.14 × 1016 cm × 0.74 × 1016 cm). The structure is also identified in the H30α recombination line. This is seen as an inclined linear feature in the position-velocity diagram, which is usually a defining characteristic of a rotating gas ring around a large mass. The gas ring has a rotating velocity of Vrot 230 km s-1 and an orbit radius of r 6 × 1015 cm. From these orbit parameters, the enclosed mass is estimated to be M IMBHsimeq 2.4× 104 M⊙. The mass is within the astrometric upper limit mass of the object adjacent to Sgr A∗. Considering IRS13E3 has an X-ray counterpart, the large enclosed mass would be supporting evidence that IRS13E3 is an IMBH. Even if a dense cluster corresponds to IRS13E3, the cluster would collapse into an IMBH within τ < 107 yr due to the very high mass density of rho 8× 1011 M⊙:pc-3. Because the orbital period is estimated to be as short as T = 2πr/Vrot ∼50-100 yr, the morphology of the observed ionized gas ring is expected to be changed in the next several decades. The mean electron temperature and density of the ionized gas are bar{Te=6800± 700:K and bar{ne=6× 105:cm-3, respectively. Then the mass of the ionized gas is estimated to be Mgas=4× 10-4 M⊙.

© The Author(s) 2018. We present high angular resolution and high sensitivity images of the “circumnuclear disk” (CND) and the surrounding region of the Milky Way Galaxy in the CS J = 2–1, SiO v = 0 J = 2–1, H13CO+ J = 1–0, C34S J = 2–1, and CH3OH JKa,Kc = 21,1–11, 0A−− emission lines using ALMA. The CND is recognized as a torus-like molecular gas with gaps in these emission lines, except for the CH3OH emission line. The inner and outer radii of the CND are estimated to be Rin ∼ 1.5 and Rout ∼ 2 pc, respectively. The velocities of the rotation and radial motion are estimated to be Vrot ∼ 115 km s−1 and Vrad ∼ 23 km s−1, respectively. The LTE molecular gas mass is estimated to be MLTE ∼ 3 × 104 M. We also found some anomalous molecular clouds in the surrounding region. One of the molecular clouds is positionally connected to part of the CND adjacent to the “western arc.” However, the cloud is seen to rotate in the opposite direction to the CND, so it could currently be falling from the outer region to the CND and being disrupted by the tidal shear of Sagittarius A∗ (Sgr A∗) because the velocity is not yet assimilated into that of the CND. Another molecular cloud is continuously connected to the tip of the “eastern arm” (EA). The velocity of this cloud is consistent with that of the ionized gas in the EA. These facts suggest that the molecular cloud is falling from the outer region to the vicinity of Sgr A∗, being disrupted by the tidal shear, and ionized by strong UV emission from the central cluster because the impact parameter of the cloud is smaller than the first cloud. These falling clouds would play an important role in transferring material from the outer region to the CND and/or the vicinity of Sgr A∗.

© 2017. The American Astronomical Society. All rights reserved. The Galactic Center is the nuclear region of the nearest spiral galaxy, the Milky Way, and contains the supermassive black hole with M M ∼ 4 106 ×, Sagittarius A∗ (Sgr A∗). One of the basic questions about the Galactic Center is whether or not Sgr A∗ is the only "massive" black hole in the region. The IRS13E complex is a very intriguing infrared (IR) object that contains a large dark mass comparable to the mass of an intermediate mass black hole (IMBH) from the proper motions of the main member stars. However, the existence of the IMBH remains controversial. There are some objections to accepting the existence of the IMBH. In this study, we detected ionized gas with a very large velocity width (DvFWZI ∼ 650 km s-1) and a very compact size (r ∼ 400 au) in the complex using the Atacama Large Millimeter/submillimeter Array (ALMA). We also found an extended component connecting with the compact ionized gas. The properties suggest that this is an ionized gas flow on the Keplerian orbit with high eccentricity. The enclosed mass is estimated to be 104 M· by the analysis of the orbit. The mass does not conflict with the upper limit mass of the IMBH around Sgr A∗, which is derived by the longterm astrometry with the Very Long Baseline Array (VLBA). In addition, the object probably has an X-ray counterpart. Consequently, a very fascinating possibility is that the detected ionized gas is rotating around an IMBH embedded in the IRS13E complex.

© The Author 2017. Published by Oxford University Press on behalf of the Astronomical Society of Japan. All rights reserved. For Permissions, please email:. The FUGIN project is one of legacy projects using a new multi-beam FOREST (four-beam receiver system on the 45 m telescope). This project aims to simultaneously investigate the distribution, kinematics, and physical properties of both diffuse and dense molecular gases in the Galaxy by observing 12 CO, 13 CO, and C 18 O J = 1-0 lines simultaneously. Mapping regions are parts of the first quadrant (10° ≤ l ≤ 50°, |b| ≤ 1°) and the third quadrant (198° ≤ l ≤ 236°, |b| ≤ 1°) of the Galaxy, where spiral arms, bar structure, and the molecular gas ring are included. This survey achieves the highest angular resolution to date (∼20″) for the Galactic plane survey in the CO J = 1-0 lines, which makes it possible to find dense clumps located farther away than the previous surveys. FUGIN will provide us an invaluable dataset for investigating the physics of the Galactic interstellar medium (ISM), particularly the evolution of interstellar gas covering galactic-scale structures to the internal structures of giant molecular clouds, such as small filaments/clumps/cores. We present an overview of the FUGIN project, the observation plan and initial results. These results reveal wide-field and detailed structures of molecular clouds, such as entangled filaments that have not been obvious in previous surveys, and large-scale kinematics of molecular gas, such as spiral arms.

© SAIt 2017. We observed the 50 km s-1 molecular cloud with a high angular resolution (∼ 1'.'5) using ALMA in the H13CO+ J=1-0, C34S J = 2-1, CS J = 2-1 and SiO v = 0 J = 2-1 emission lines. This cloud is a candidate for the massive star forming region induced by cloudcloud collision (CCC). We newly found a massive dense clump (DC1) with a size of ∼ 0.3 pc in the CCC region of the cloud in the H13CO+ J=1-0 map. The DC1 seems to be located on a line where the four HII regions line up. Furthermore, the DC1 has a broad velocity width covering ∼ 30 km s-1 and ∼ 60 km s-1 components in the CS J = 2-1 map; the 30 km s-1 component has filamentary structures and the 60 km s-1 one a sheet-like structure. From the position-velocity diagrams of the H13CO+ J=1-0 and CS J = 2-1 lines and the intensity ratio of T(SiO v = 0 J = 2-1)/T(H13CO+ J = 1-0), i.e., a shock tracer, we consider that the DC1 has formed by the CCC between the filaments and the sheet-like gas. The LTE mass and virial parameter of the DC1 is estimated to be ∼ 1.3 x 104 MO; and ∼ 5, respectively. These facts suggest that the DC1 is likely in a gravitationally bound state and may start massive star formation. We propose a scenario that the CCC induced the massive star formation in the HII region A ∼ 105 years ago and now causes the formation and collapse of the DC1; the clump would evolve to an HII region within ∼ 105 years.

© 2017 International Astronomical Union. We have observed the Galactic Center 50km/s molecular cloud (50MC) with ALMA to search for filamentary structures. In the CS J=2-1 emission line channel maps, we succeeded in identifying 27 molecular cloud filaments using the DisPerSE algorithm. This is the first attempt of filament-finding in the Galactic Center Region. These molecular cloud filaments strongly suggest that the molecular cloud filaments are also ubiquitous in the molecular clouds of the Galactic Center Region.

© The Author 2016. Published by Oxford University Press on behalf of the Astronomical Society of Japan. We present continuum images of the Galactic center mini-spiral in the 100, 250, and 340 GHz bands with analysis of the Cy.0 data acquired from the Atacama Large Millimeter/submillimeter Array (ALMA) archive. Good u-v coverage of the data and the self-calibration method give us the opportunity to obtain dynamic ranges of over 2 104 in the resultant maps of the 250 and 340 GHz bands. In particular, the image of the 340 GHz band has high dynamic ranges unprecedented in sub-millimeter waves. The angular resolutions attained are 1. 57 1. 33 in the 100 GHz band, 0. 63 0. 53 in the 250 GHz band, and 0. 44 0. 38 in the 340 GHz band, respectively. The continuum images clearly depict the mini-spiral, which is an ionized gas stream in the vicinity of SgrA. We found a tight correlation between the dust emission peaks and the OB/WR stars in the northern arm of the mini-spiral. The core mass function of the dust cores identified by the clumpfind algorithm would obey the flat power-law dN/dM M1.5±0.4 on the high-mass side. These support the scenario that the star-forming cloud has fallen into the immediate vicinity of SgrA for the origin of the central cluster.

© The Author 2015. Published by Oxford University Press on behalf of The Royal Astronomical Society. We present results from a high-resolution wide-field imaging observation of the Central Molecular Zone (CMZ) in H13CO+ J = 1-0 and SiO v = 0, J = 2-1 emission lines using the 45-m telescope at the Nobeyama Radio Observatory in order to depict the high-density molecular gas mass distribution and explore molecular gas affected by interstellar shocks. By using the clumpfind algorithm we identify 114 molecular clumps in the H13CO+ data cube. The clump mass function (CMF) can be described by a power law (dN/dM ∝ M-γ, with γ ≃ 2) in the range of 5 × 103 < Mclump < 2 × 104 M⊙. The brightness temperature ratio RT = T(SiO)/T(H13CO+) indicates the strength of the shock. The Sgr B2 complex has several expanding shell-like structures with a large velocity-width (ΔV > 50 km s-1). They correspond to the high brightness temperature ratio area (RT ≲ 8). A Large Velocity Gradient model analysis with the RADEX program confirms the enhancement of SiO molecules in the shells. On the other hand, there is no such large shell with a high ratio in the Sgr A complex. A hollow hemispherical structure is found in the l-b-v data cube of the Sgr B2 complex. The central part of the structure has a high ratio (RT ≲ 8). The ratio decreases with proximity to the outer area. The properties are consistent with those expected from simulations of cloud-cloud collisions. The structure is probably a site of ongoing cloud-cloud collision.

© 2015. The American Astronomical Society. All rights reserved. In order to explore any change caused by the G2 cloud approaching, we have monitored the flux density of Sgr A∗ at 22 GHz from 2013 February to 2014 August with a sub-array of the Japanese Very Long Baseline Interferometry Network. The observation period included the expected periastron dates. The number of observation epochs was 283 days.We have observed no significant microwave enhancement of Sgr A∗ in the whole observation period. The average flux density in the period is Sv = 1.23 ± 0.33 Jy. The average is consistent with the usually observed flux density range of Sgr A∗ at 22 GHz.

We identified a half-shell like feature with a high emission line ratio of T(SiO J = 2 - 1)/T((HCO+)-C-13 J = 1 - 0)similar to 6 - 8 and large velocity width in the Galactic Center 50 km s(-1) molecular cloud, which is conspicuous in the Sgr A region and harbors an active star-forming site. These properties suggest that the feature is originated by a cloud-cloud collision. We analyzed the CS J = 1 - 0 emission line data obtained by Nobeyama Millimeter Array to explore the molecular cloud cores in the cloud. The core mass function in the feature has a flat slope and is not truncated up to similar to 2000M circle dot. This may a sign of massive star formation induced by the cloud-cloud collision.

We searched the time lag between the intra-day variables (IDVs) of Sagittarius A* at 22, 43, and 86 GHz bands using the Korean VLBI Network (KVN). The time lags between the IDV flare peaks at 22 and 43 GHz are reported, and they suggest that the flare emissions come from adiabatically expanding plasma blobs, ejected close to the Galactic center black hole. We searched the time lags between light curves at 90 and 102 GHz using the Nobeyama Millimeter Array, but could not find significant time lags. In order to detect the diversity of the time lags of Sgr A* flares, we performed observations of Sgr A* in the 22, 43, and 86 GHz bands using the KVN in the winter of 2013. Because the receiver system of KVN can observe Sgr A* in these three bands simultaneously, the KVN is very useful to detect the time lags of Sgr A* flares. Copyright © International Astronomical Union 2014.

We present the analysis of flux variations of Sgr A* at millimeter wavelengths based on the long-term monitoring project spanning over a decade using the Nobeyama Millimeter Array. We investigate basic characteristics of the flux variability using some standard parameterizations of the data. Such basic properties of the flux variations in the mm-regime can provide valuable information not only for its underlying mechanisms in general but also for understanding observed radio/mm flux measurements during an accretion event. Copyright © International Astronomical Union 2014.

We have been monitoring the flux density of Sagittarius A* (Sgr A*) at 22 GHz since DOY=42 (11 Feb. 2013) with a sub-array of the Japanese VLBI Network in order to search the increase of 22-GHz emission from Sgr A* induced by the interaction of the G2 cloud with the accretion disk. The flux densities observed until DOY=322 (18 Nov. 2013) are consistent with the previously observed values before the approaching of the cloud. We have detected no large flare during this period. Copyright © International Astronomical Union 2014.

We present results from a high-resolution wide-field imaging observation of the central molecular zone (CMZ) in (HCO+)-C-13 J = (1 - 0) and SiO v = 0, J = (2 - 1) emission lines by using the Nobeyama 45-m telescope in order to depict the high-density molecular gas mass distribution and explore molecular gas affected by interstellar shocks. We found a candidate for ongoing cloud-cloud collision in the Sgr B2 complex. This is identified as a hollow paraboloid-like structure in the l-b-v data cube of both emission lines. The central part of the feature is denser and warmer than the outer envelope and contains a vast amount of shocked molecular gas. These properties are consistent with those expected from simulations of cloud-cloud collisions in the CMZ.

A compact gas cloud G2 is predicted to reach the pericenter of its orbit around the supermassive black hole (SMBH) of our Galaxy, Sagittarius A*. This event will give us a rare opportunity to observe the interaction between the SMBH and the gas around it. We report on the result of a fully three-dimensional simulation of the evolution of G2 during the first pericenter passage. The strong tidal force from the SMBH stretches the cloud along its orbit, and strongly compresses it in the vertical direction, resulting in its heating up and flaring up. The bolometric luminosity will reach a maximum of ∼ 100 Lȯ. This flare should be easily observed in the near-IR. © The Author 2014. Published by Oxford University Press on behalf of the Astronomical Society of Japan. All rights reserved.

© 2014 The Author 2014. Published by Oxford University Press on behalf of the Astronomical Society of Japan. All rights reserved. The 22∈GHz H2O maser in Orion∈KL has shown extraordinary burst events in 1979-1985 and 1998-1999, sometimes called supermaser. We have conducted monitoring observations of the supermaser in Orion∈KL using VERA (VLBI Exploration of Radio Astrometry) in the current third burst since 2011 March. Three flux maxima are detected in 2011 and 2012 with rising and falling timescales of 2-7 months. Time variations of the supermaser seem symmetric for all of the active phases. The maximum total flux density of 135000∈Jy is observed in 2012 June while it is still one order of magnitude lower than those in previous bursts. The supermaser consists of two spatially different components at different velocities. They are elongated along a northwest-southeast direction perpendicular to the low-velocity outflow driven by Source I. Proper motions of the supermaser features with respect to Source I are measured toward west and southwest directions, almost parallel to the low-velocity outflow. The flux density and linewidth show an anti-correlation as expected for an unsaturated maser emission. The supermaser is located close to the methylformate (HCOOCH3) line and continuum emission peaks in the Orion Compact Ridge detected by ALMA (Atacama Large Millimeter/Submillimeter Array). The broader velocity range of the weak HCOOCH3 emission at the supermaser position would be evidence of a shock front. On the other hand, the 321∈GHz H2O line is not detected at the position of the supermaser. It can be explained qualitatively by one of the theoretical H2O excitation models without extraordinary conditions. Our results support a scenario that the supermaser is excited in the dense gas interacting with the low-velocity outflow in the Compact Ridge. The extremely high flux density and its symmetric time variation for rising and falling phases could be explained by a beaming effect during the amplification process rather than changes in physical conditions.

We performed observations of the flux densities of SgrA* at 90 and 102 GHz in order to detect any time lag between these frequencies using the Nobeyama Millimeter Array, which was previously reported at lower frequencies. We detected a radio flare during the observation period on 2005 April 6, and calculated the z -transformed discrete correlation function between the light curves. No time lag between these frequencies was detected. If the expanding plasma model, which explains a time lag at lower frequencies, is valid, the light curve at 90 GHz would be delayed in respect to that at 102 GHz. This result suggests that plasma blobs ejected close to the Galactic center black hole may be widely diverse, especially in optical thickness. Another possibility is that a major portion of the flux above 100 GHz does not originate in blobs. © 2013. Astronomical Society of Japan.

Large deployable antennas with a mesh surface woven by fine metal wires are an important technology for communications satellites and space radio telescopes. However, it is difficult to make metal mesh surfaces with sufficient radio-frequency (RF) performance for frequencies higher than millimeter waves. In this paper, we present the RF performance of metal mesh surfaces at 43 GHz. For this purpose, we developed an apparatus to measure the reflection coefficient, transmission coefficient, and radiative coefficient of the mesh surface. The reflection coefficient increases as a function of the metal mesh surface tension, whereas the radiative coefficient decreases. The anisotropic aspects of the reflection coefficient and the radiative coefficient are also clearly seen. They depend on the front and back sides of the metal mesh surface and the rotation angle. The transmission coefficient was measured to be almost constant. The measured radiative coefficients and transmission coefficients would cause significant degradation of the system noise temperature. In addition, we carried out an astronomical observation of a well-known SiO maser source, R Cas, by using a metal mesh mirror on the NRO 45-m radio telescope Coudé system. The metal mesh mirror considerably increases the system noise temperature, and slightly decreases the peak antenna temperature. These results are consistent with laboratory measurements. © 2013. Astronomical Society of Japan.

We present the results of astrometry with VERA of the 22 GHz H2O maser burst in Orion KL started since 2011 February. According to the absolute positions and proper motions of the bursting H2O maser features, it is most likely that the outflow from the radio Source I or another young stellar object in the Compact Ridge is a possible origin of the burst. In addition, we report the first detection of the 232 GHz vibrationally excited H2O maser in star-forming regions by using the ALMA Science Verification data of Orion KL. The 232 GHz H2O maser is detected toward the Source I and its spectral profile shows a double-peaked structure analogous to the 22 GHz H2O and 43 GHz SiO masers. Thus, the 232 GHz H2O maser would be excited in the dense and hot gas around the Source I as in the case of other maser lines.

We present the statistical properties of molecular clumps in the Galactic center 50 km s-1 molecular cloud (GCM- 0.02-0.07) based on observations of the CS J = 1-0 emission line with the Nobeyama Millimeter Array. In the cloud, 37 molecular clumps with local thermodynamic equilibrium (LTE) masses of 2 × 102-6 × 103Moci; were identified by using the clumpfind algorithm. The velocity widths of the molecular clumps are about five-fold those of Galactic disk molecular clouds with the same radius. The virial-theorem masses are three-fold the LTE masses. The mass and size spectra can be described by power laws of dN=dM ∝ M -2:6±0:1 (M ≳ 900 Mocir) and dN=dR ∝ R-5:9±03 (R ≳ 0.35 pc), respectively. The statistical properties of the region interacting with the Sgr A East shell and those of the non-interacting part of the cloud are significantly different. The interaction probably makes the mass function steeper, from dN=dM ∝ m-2:0±0:1 in the non-interacting part to dN=dM ∝ M-4:0±0:2 in the interacting region. On the other hand, the interaction presumably truncates the size spectrum on the larger side of R ∼ 0.4 pc. © 2012. Astronomical Society of Japan. 1 Nobeyama Radio Observatory is a branch of the National Astronomical Observatory, National Institutes of Natural Sciences, Japan.

We present the statistical properties of molecular clumps in the Galactic center 50 km s-1 molecular cloud based on observations of the CS J=1-0 emission line with the Nobeyama Millimeter Array. The CMF and size spectrum for the whole cloud can be described by power laws of dN/dM ∞ M-2.6 ± 0.1 and dN/dR ∞ R-5.9±0.3, respectively. The CMF observed in the interacting part with the Sgr A East steepens to dN/dM ∞ M -4.0±0.2. On the other hand, the interaction presumably truncates the size spectrum on the larger side of R ∼ 0.4 pc. © 2013 International Astronomical Union.

In 2011 February, a burst of the 22 GHz H2O maser in Orion KL was reported. In order to identify the bursting maser features, we have been carrying out observations of the 22 GHz H2O maser in Orion KL with VERA, a Japanese VLBI network dedicated for astrometry. The bursting maser turns out to consist of two spatially different features at 7.58 and 6.95 km s-1. We determine their absolute positions and find that they are coincident with the shocked molecular gas called the Orion Compact Ridge. We tentatively detect the absolute proper motions of the bursting features toward the southwest direction, perpendicular to the elongation of the maser features. It is most likely that the outflow from the radio source I or another young stellar object interacting with Compact Ridge is a possible origin of the H2O maser burst. We will also carry out observations with ALMA in the cycle 0 period to monitor the submillimeter H2O maser lines in the Orion Compact Ridge region. These follow-up observations will provide novel information on the physical and chemical properties of the mastering region. Copyright © International Astronomical Union 2012.

Cygnus X-3 (Cyg X-3) is a well-known microquasar with relativistic jets. It is especially famous for its giant radio outbursts, which have been observed once every few years since their first discovery. Each giant outburst presumably consists of a series of short-duration flares. The physical parameters of the flares in the giant outbursts are difficult to derive because the successive flares overlap. Here, we report on isolated flares in the quiescent phase of Cyg X-3, as observed at 23, 43, and 86 GHz with the 45-m radio telescope at Nobeyama Radio Observatory. The observed flares have small amplitude (0.5-2 Jy) and short duration (1-2 hr). The millimeter fluxes rapidly increase, and then exponentially decay. The lifetime of the decay is shorter at higher frequency. The radio spectrum of Cyg X-3 during the flares is flat or inverted around the peak flux density. After that, the spectrum gradually becomes steeper. The observed characteristics are consistent with those of an adiabatic expanding plasma. The brightness temperature of the plasma at the peak is estimated to be T-B greater than or similar to 1 x 10(11) K. The magnetic field in the plasma is calculated to be 0.2 less than or similar to H less than or similar to 30G.

In 2011 February, a burst event of the H2O maser in Orion KL (Kleinmann-Low object) has started after a 13year silence. This is the third time such phenomena has been detected in Orion KL, followed by the events in 1979-1985 and 1998. We have carried out astrometric observations of the bursting H2O maser features in Orion KL with the VLBI Exploration of Radio Astrometry (VERA), a Japanese very long baseline interferometry network dedicated for astrometry. The total flux of the bursting feature at the local standard of rest (LSR) velocity of 7.58kms-1 reaches 4.4 × 104Jy in 2011 March. The intensity of the bursting feature is three orders of magnitude larger than that of the same velocity feature in the quiescent phase in 2006. Two months later, another new feature appears at the LSR velocity of 6.95kms-1 in 2011 May, separated by 12mas north of the 7.58kms-1 feature. Thus, the current burst occurs at two spatially different features. The bursting masers are elongated along the northwest-southeast direction as reported in the previous burst in 1998. We determine the absolute positions of the bursting features for the first time ever with a submilliarcsecond (mas) accuracy. Their positions are coincident with the shocked molecular gas called the Orion Compact Ridge. We tentatively detect the absolute proper motions of the bursting features toward the southwest direction. It is most likely that the outflow from the radio source I or another young stellar object interacting with the Compact Ridge is a possible origin of the H2O maser burst. © 2011. The American Astronomical Society. All rights reserved.

We present results of a high-resolution wide-field mapping observation of the Sagittarius A (Sgr A) molecular cloud complex in (HCO+)-C-13 J = 1-0 and thermal SiO J = 2-1 emission lines with the 25-beam receiver of the 100 GHz band operating on the Nobeyama Radio Observatory 45-m telescope. The mapping area covers a 0 degrees 5 x 0 degrees 5 area involving several named molecular clouds, for example GCM -0.02-0.07, GCM -0.13-0.08, GCM 0.11-0.11, the Sickle molecular cloud, the Arched filaments molecular cloud, and so on. The data have an effective angular resolution of 26 ''. The (HCO+)-C-13 emission line is a famous tracer of molecular gas mass because the line is optically thin, even in the Galactic center region, and is not emphasized by shock. The emission line presents a clumpy distribution of the molecular cloud. The averaged fractional abundance in the Sgr A complex is N((HCO+)-C-13)/N-H2 similar or equal to (1.8 +/- 0.4) x 10(-11), comparing the LTE mass and the virial theorem mass. The SiO emission line is a famous and reliable tracer of shocked molecular gas. We find many molecular clouds that are remarkable only in the SiO emission line. Such molecular clouds have a large velocity width of up to 60 km s(-1). The brightness temperature ratio is up to TB(SiO)/TB((HCO+)-C-13) less than or similar to 8. The features are dominated by shock SiO-enriched gas. In such clouds, the ratio of the fractional abundance of SiO and (HCO+)-C-13 molecules is X (SiO)/ X ((HCO+)-C-13) similar to 100. The features are presumably made by supernova remnants. We found a prototypical example in GCM -0.02-0.07. It has two distinct structures. One is a ridge-like structure contacting with the Sgr A East shell; another is an expanding shell-like structure. There is a wide-velocity width ridge of SiO-enriched gas in GCM 0.11-0.11, which is adjacent to Vertical filaments. This suggests that the collision with the molecular cloud accelerates relativistic electrons, which, illuminate the Vertical filaments-Polarized Plumes complex.

In the construction of a space radio telescope, it is essential to use materials with a low noise factor and high mechanical robustness for the antenna surface. We present the results of measurements of the reflection performance of two candidates for antenna surface materials for use in a radio telescope installed in a new millimeter-wave astronomical satellite, ASTRO-G. To estimate the amount of degradation caused by fluctuations in the thermal environment in the projected orbit of the satellite, a thermal cycle test was carried out for two candidates, namely, copper foil carbon fiber reinforced plastic (CFRP) and aluminum-coated CFRP. At certain points during the thermal cycle test, the reflection loss of the surfaces was measured precisely by using a radiometer in the 41-45GHz band. In both candidates, cracks appeared on the surface after the thermal cycle test, where the number density of the cracks increased as the thermal cycle progressed. The reflection loss also increased in proportion to the number density of the cracks. Nevertheless, the loss of the copper foil surface met the requirements of ASTRO-G at the end of the equivalent life, whereas that of the aluminum-coated surface exceeded the maximal value in the requirement even before the end of the cycle. © 2011. Astronomical Society of Japan.

This paper reviews the recent progress in the study of the intra-day variability (IDV) of Sagitarrius A* (Sgr A*), the best known supermassive black hole candidates with a dark mass concentration of 4 × 106M⊙ at the center of our galaxy. © 2011 Indian Academy of Sciences.

We are planning to construct a VLBI system in the Andes dedicated only to the detection of the event horizon of the SgrA* black hole.

Multimode horns were developed for 8.4GHz, 22GHz, 43GHz receiver systems of ASTRO-G/VSOP-2 satellite for Space-VLBI, and for 6.7GHz of VERA 20m radio telescopes of National Astronomical Observatory in JAPAN and 25m Shanghai Radio telescope in China. Rational bandwidth of these horns in low cross polar level are 20-30%, and their thin walls without corrugation and shortened length are the best for the satellite use. Also, wideband feeds will be presented, which are now developing for SKA and VLBI2010, which is a kind of Tapered Slot Antenna or other of traveling wave antenna. © 2011 IEEE.

We present results of a high-resolution wide-field mapping observation of Central Molecular Zone (CMZ) in SiO v = 0, J = 2 - 1 and (HCO+)-C-13 J = 1 0 emission lines using the Nobeyama Radio Observatory 45-m telescope and the 25-beam receiver of 100 GHz band in order to explore molecular gas affected by shock in the regions and depict the molecular gas mass distribution. The mapping area covers an 1.5 degrees x0.5 degrees area involving several named molecular clouds, for example the Sgr A molecular cloud complex, the Sgr B2 molecular cloud, and so on. The SiO emission line is known as a privileged tracer of shocked molecular gas. We find many molecular clouds remarkable only in SiO emission line. The molecular clouds have large velocity width up to 60 km s(-1). The brightness temperature ratio is high up to T-B(SiO)/T-B ((HCO+)-C-13) <= 8. The features are dominated by shock SiO-emphasized gas. In such clouds, the ratio of fractional abundance of SiO and (HCO+)-C-13 molecules is increased to X(SiO)/X((HCO+)-C-13) >= 30. Meanwhile, the (HCO+)-C-13 emission line is a famous tracer of molecular gas mass. (HCO+)-C-13 emission line presents clumpy distribution of molecular cloud. The averaged fractional abundance in the region is X((HCO+)-C-13) = 1 x 10(-10). The total molecular mass of the CMZ is M-LTE = 17 +/- 8 x 10(6)M(circle dot).

We present flaring emission observations from the Galactic Center compact radio source Sgr A* with the Australia Telescope Compact Array at mm wavelengths. Careful calibrations of both elevation-dependent and time-dependent gains have enabled us to establish the variability behavior of Sgr A*. Sgr A* was found to be very active, and several flares were detected at 3 mm wavelength during our observations from 2005 to 2008. On 2008 October 3, we detected flare emission quasi-simultaneously at 3 and 7 mm wavelengths, with the 3 mm flare leading 7 mm by about 1 hr. The observed time delay between 3 and 7 min wavelength seems to support the expanding plasmon model.

Cyg X-3 is a well-known microquasar with a bipolar relativistic jet. Its famous giant radio outbursts have been repeated once every several years. However, the behavior of the millimeter-wave emission has remained unclear because of limitations of time resolution in previous observations. We report here on millimeter wave observations of Cyg X-3 experiencing giant outbursts with one of the finest time resolutions. We have found a series of shortlived flares with amplitudes of 1-2 Jy in the millimeter light curve of the 2008 April-May outburst. They have flat spectra at around 100 GHz. We have also found abrupt and large amplitude flux density changes with e-folding time of 3.6min or less. The source size of Cyg X-3 is constrained to within 0.4 AU, and the brightness temperature is estimated to be TB ≳ 1 × 10 11 K. © 2010. Astronomical Society of Japan.

We identified the double helix nebula (DHN) found by the Spitzer Space Telescopein the Galactic center region as a highly polarized feature at 10 GHz with the Nobeyama 45 m telescope. The DHN is located near the north end of the polarized plumes. The position angles of Faraday rotation corrected B vectors in the DHN are presumably along the twisting IR filaments. The linear polarization degree of the DHN is as large as p = 10%, and reaches p = 15% ± 2% at the radio polarization peak of the DHN. This means that the DHN has highly ordered magnetic field with synchrotron-emitting relativistic electrons. © 2010. The American Astronomical Society. All rights reserved.

Space VLBI (very long baseline interferometry) mission, ASTRO-G, will be launched in 2013 by Japan Aerospace Exploration Agency (JAXA). ASTRO-G is a follow-on mission of HALCA (VSOP) mission in 1990s, which was the world first space VLBI mission. ASTRO-G will consists of a huge synthetic aperture with diameter of 35,000 Km together with radio antennas in the ground. They will achieve the world highest angular resolution imaging by means of 43 GHz observation. This paper describes the advanced key technologies of ASTRO-G such as the 9 m deployable antenna with very accurate surface, the fast rest - to - rest attitude maneuver, and the precision orbit determination above NAVSTAR&#039;s orbits. These advance technologies lead ASTRO-G mission to the astronomical observation with the world highest angular resolution.

© 2009. The American Astronomical Society. All rights reserved. We have performed monitoring observations of the 3 mm flux density toward the Galactic center compact radio source Sagittarius A∗ (Sgr A∗) with the Australia Telescope Compact Array since 2005 October. Careful calibrations of both elevation-dependent and time-dependent gains have enabled us to establish the variability behavior of Sgr A∗. Sgr A∗ appeared to undergo a high and stable state in the 2006 June session, and a low and variable state in the 2006 August session. We report the results, with emphasis on two detected intraday variation events during its low states. One is on 2006 August 12 when Sgr A∗ exhibited a 33% fractional variation in about 2.5 hr. The other is on 2006 August 13 when two peaks separated by about 4 hr, with a maximum variation of 21% within 2 hr, were seen. The observed short timescale variations are discussed in light of two possible scenarios, i.e., the expanding plasmon model and the sub-Keplerian orbiting hot spot model. The fitting results indicate that for the adiabatically expanding plasmon model, the synchrotron cooling cannot be ignored, and a minimum mass-loss rate of 9.7 × 10-10 MΘ yr-1 is obtained based on parameters derived for this modified expanding plasmon model. Simultaneous multiwavelength observation is crucial to our understanding of the physical origin of rapid radio variability in Sgr A∗.