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The Atacama Large Millimeter/submillimeter Array remains the largest mm radio interferometer observatory world-wide. It is now conducting its 11th observing cycle. In our previous paper presented at this conference series in 2020, we outlined a number of possible improvements to the ALMA end-to-end observing and data processing procedures which could further optimize the uv coverage and thus the image quality while at the same time improving the observing efficiency. Here we report an update of our results refining our proposed adjustments to the scheduling and quality assurance processes. In particular we present new results on ways to assess the uv coverage of a given observation efficiently, methods to define and measure the maximum recoverable angular scale, and on the robustness of the deconvolution in the final interferometric imaging process w.r.t. defects in the uv coverage. Finally we present the outline of a design for integrating uv coverage assessment into the control and processing loop of observation scheduling. The results are applicable to all radio interferometers with more than approx. 10 antennas., Comment: 12 pages, 8 figures, to be published in the proceedings of SPIE Astronomical Telescopes and Instrumentation, 2024, Yokohama, paper no. 13098-27

Atacama Large Millimeter/Submillimeter Array (ALMA) is promising to be a powerful tool for precision astrometry of the area around Sagittarius A$^\ast$ (Sgr A$^\ast$) because it has the high angular resolution, high sensitivity, and wide field of view. We have observed the area including the Nuclear Star Cluster at 230 GHz with ALMA in October 2017. The angular resolution is ~0.03". We determined the relative positions to Sgr A$^\ast$ of 65 compact objects in the area with the accuracy of 0.001". We also analyzed the similar ALMA archival data obtained in June 2019 and determined the 64 relative positions in these objects. We derived the proper motions relative to Sgr A$^\ast$ by comparing these positions. The derived proper motions are roughly described with both clockwise and counterclockwise rotations around Sgr A$^\ast$. The rotation velocities are reproduced by Kepler orbits bounded around Sgr A$^\ast$. Moreover, the proper motions include co-moving clusters for example IRS13E and IRS13N. The positions and proper motions are almost consistent with those by previous infrared observations. Therefore the observational demonstrations would prove that ALMA is a powerful tool for precision astrometry of the region., Comment: 29 pages, 10 figures, 3 tables; Accepted for publication in PASJ

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., Comment: 26pages, 24figures, 3tables, accepted for publication in PASJ

We investigate dynamical states of grand-design spiral arms in three local galaxies: M51, NGC3627 and NGC628. Based on linear perturbation analysis considering multiple components in the galaxies, we compute instability parameters of the spiral arms using their observational data and argue whether the arms will fragment by their self-gravity. Our analysis utilises observations of carbon monoxide (CO), 21-centimetre line emission and multi-band photometric images for molecular gas, atomic gas and stellar components in the arms, respectively. We find that the grand-design arms of these galaxies indicate marginally stable states, and hence they are not on the way to fragment. We consider this to be consistent with the commonness of spiral galaxies and the relative rarity of fragmented discs at low redshifts. In the analysis, molecular gas is the dominant component to determine the (in)stability of the arms, whereas atomic gas and stars are far less important. Therefore, the results of our analysis are sensitive to an assumed CO-to-H$_{\rm 2}$ conversion factor. If we assume a typical scatter of the measurements and admit nearly twice as large a conversion factor as our fiducial value, our analysis results in predicting the instability for the spiral arms. More sophisticated determination of the conversion factor is required for more accurate analysis for the (in)stability of spiral arms., Comment: 14 pages, 10 figures. Accepted to MNRAS

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 C$^{32}$S $J=1-0$ and SiO $v=0~J=2-1$ emission lines. We found candidates being 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 C$^{32}$S $J=2-1$, C$^{34}$S $J=2-1$, SiO $v=0~J=2-1$, H$^{13}$CO$^+ J=1-0$, 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 (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 H42$\alpha$ recombination line. They are detected in the SO emission line, and would be "Hot Molecular Core (HMC)"s. Because the LTE 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 poloidal magnetic field. Because the strength of the magnetic field is estimated to be $\sim m$Gauss using the CF 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., Comment: 40 pages, 14 figures, 2 tables, accepted for publication in PASJ

The Galactic Center Lobe (GCL) is a peculiar object widely protruding from the Galactic plane toward the positive Galactic latitude, which had been found toward the Galactic Center (GC) in the early days of the radio observation. The peculiar shape has suggested any relation with historical events, star burst, large explosion and so on in the GC. However, the issue whether the GCL is a single large structure located in the GC region is not yet settled conclusively. In the previous observations, the silhouette against the low frequency emission was found in the western part of the GCL (WPGCL), This suggests that the part is located in front of the GC region. On the other hand, the LSR velocity of the radio recombination line toward it was found to be as low as 0 kms$^{-1}$. However, these observations cannot determine the exact position on the line-of-sight. There is still another possibility that it is in the near side area of the GC region. In this analysis, we compare these results with the visual extinction map toward the GC. We found that the distribution of the visual extinction larger than 4 mag. clearly corresponds to the silhouette of the WPGCL. The WPGCL must be located at most within a few kpc from us and not in the GC region. This would be a giant HII region in the Galactic disk., Comment: 10 pages, 3 figures, Accepted for publication in PASJ

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$^{\ast}$., Comment: 9 pages, 2 figures, 1 table, Accepted for publication in PASJ

IRS 7 is an M red supergiant star which is located at $5".5$ north of Sagittarius A$^\ast$. We detected firstly the continuum emission at 340 GHz of IRS 7 using ALMA. The total flux density of IRS 7 is $S_\nu=448\pm45 \mu$Jy. The flux density indicates that IRS 7 has a photosphere radius of $R=1170\pm60 ~R_\odot$, which is roughly consistent with the previous VLTI measurement. We also detected a shell like feature with north extension in the H30$\alpha$ recombination line by ALMA. The electron temperature and electron density of the shell like structure are estimated to be $\bar{T}^\ast_{\mathrm e}=4650\pm500$ K and $\bar{n}_{\mathrm e}=(6.1\pm0.6)\times10^4$ cm$^{-3}$, respectively. The mass loss rate is estimated to be $\dot{m} \sim 1\times 10^{-4} M_\odot$ yr$^{-1}$, which is consistent with a typical mass loss rate of a pulsating red supergiant star with $M=20-25 M_\odot$. The kinematics of the ionized gas would support the hypothesis that the shell like structure made by the mass loss of IRS 7 is supersonically traveling in the ambient matter toward the south. The brightened southern half of the structure and the north extension would be a bow shock and a cometary-like tail structure, respectively., Comment: 15 pages, 5 figures Accepted for publication in PASJ

We have observed the compact HII region complex nearest to the dynamical center of the Galaxy, G-0.02-0.07, using ALMA in the H42a recombination line, CS J=2-1, H13CO+ J=1-0, and SiO v=0, J=2-1 emission lines, and 86 GHz continuum emission. The HII 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 absorption features in the molecular emission lines show that HII-A, B and C are located on the near side of the 50 km/s Molecular Cloud (50MC) but HII-D is located on the far side. The electron temperatures and densities range Te=5150-5920 K and ne=950-2340 cm-3, respectively. The electron temperatures on the bright-half are slightly lower than those on the dark-half, while the electron densities on the bright-half are slightly higher than those on the dark-half. The HII regions are located on the molecular filaments in the 50MC. They have already broken through the filaments and are growing in the surrounding molecular gas. There are some shocked molecular gas components around the HII regions. From line width of the H42a recombination line, the expansion velocities from HII-A to HII-D are estimated to be Vexp=16.7, 11.6, 11.1, and 12.1 km/s, respectively. The expansion timescales from HII-A to HII-D are estimated to be Tage~1.4x0^4, 1.7x10^4, 2.0x10^4, and 0.7x10^4 years, 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. The positional relation among the HII regions, the SiO molecule enhancement area, and Class-I maser spots suggest that the 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 trigger the massive star formation., Comment: 33 pages, 13 figures, 3 tables. Accepted for publication in PASJ

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 H30$\alpha$ 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 $0".093\pm0".006\times 0".061\pm0".004$ ( $1.14\times10^{16}$ cm $\times 0.74\times10^{16}$ cm). The structure is also identified in the H30$\alpha$ 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 $V_\mathrm{rot}\simeq230$ km s$^{-1}$ and an orbit radius of $r\simeq6\times10^{15}$ cm. From these orbit parameters, the enclosed mass is estimated to be $M_{\mathrm{IMBH}}\simeq2.4\times10^4$ $M_\odot$. The mass is within the astrometric upper limit mass of the object adjacent to Sgr A$^{\ast}$. 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 $\tau<10^7$ years due to the very high mass density of $\rho \gtrsim8\times10^{11} M_\odot pc^{-3}$. Because the orbital period is estimated to be as short as $T=2\pi r/V_\mathrm{rot}\sim 50-100$ 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 $\bar{T}_{\mathrm e}=6800\pm700$ K and $\bar{n}_{\mathrm e}=6\times10^5$ cm$^{-3}$, respectively. Then the mass of the ionized gas is estimated to be $M_{\mathrm{gas}}=4\times10^{-4} M_\odot$., Comment: accepted for publication in PASJ. 13 pages, 4 figures

We present the high angular resolution and high sensitivity images of the "Circum-Nuclear Disk (CND)" and its surrounding region of Milky Way Galaxy in the CS J=2-1, SiO v=0 J=2-1, H^13CO^+ J=1-0, C^34S J=2-1, and CH_3OH J_{K_a, K_c}=2_{1,1}-1_{1,0}A_{--} emission lines using ALMA. The CND is recognized as a torus-like molecular gas with gaps in these emission lines except for the CH_3OH emission line. The inner and outer radii of the CND are estimated to be R_in~1.5 and R_out~2 pc, respectively. The velocities of the rotation and radial motion are estimated to be V_rot~115 km s^-1 and V_rad~23 km s^-1, respectively. The LTE molecular gas mass is estimated to be M_LTE~3x10^4 Mo. We also found some anomalous molecular clouds in the surrounding region. One of the molecular clouds is positionally connected to a part of the CND adjacent to the "Western Arc". However, the cloud is seen to rotate in the opposite direction to the CND. The molecular cloud would be falling currently 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*., Comment: 31 pages, 12 figures, Accepted for publication in PASJ

3C 84 (NGC 1275) is a well-studied mis-aligned Active Galactic Nucleus (AGN), which has been active in Gamma rays since at least 2008. We have monitored the source at four wavelengths (14 mm, 7 mm, 3 mm and 2 mm) using the Korean VLBI network (KVN) since 2013 as part of the interferometric monitoring of $\gamma$-ray bright AGN (iMOGABA) program. 3C 84 exhibits bright radio emission both near the central supermassive black hole (SMBH) feature known as C1 and from a moving feature located to the south known as C3. Other facilities have also detected these short-term variations above a slowly rising trend at shorter wavelengths, such as in Gamma ray and 1 mm total intensity light-curves. We find that the variations in the $\gamma$ rays and 1 mm total intensity light-curves are correlated, with the $\gamma$ rays leading and lagging the radio emission. Analysis of the 2 mm KVN data shows that both the Gamma rays and 1 mm total intensity short-term variations are better correlated with the SMBH region than C3, likely placing the short-term variations in C1. We interpret the emission as being due to the random alignment of spatially separated emission regions. We place the slowly rising trend in C3, consistent with previous results. Additionally, we report that since mid-2015, a large mm-wave radio flare has been occurring in C3, with a large Gamma ray flare coincident with the onset of this flare at all radio wavelengths., Comment: 12 pages, 12 figures, accepted to MNRAS

Atmospheric propagation effects at millimeter wavelengths can significantly alter the phases of radio signals and reduce the coherence time, putting tight constraints on high frequency Very Long Baseline Interferometry (VLBI) observations. In previous works, it has been shown that non-dispersive (e.g. tropospheric) effects can be calibrated with the frequency phase transfer (FPT) technique. The coherence time can thus be significantly extended. Ionospheric effects, which can still be significant, remain however uncalibrated after FPT as well as the instrumental effects. In this work, we implement a further phase transfer between two FPT residuals (i.e. so-called FPT-square) to calibrate the ionospheric effects based on their frequency dependence. We show that after FPT-square, the coherence time at 3 mm can be further extended beyond 8~hours, and the residual phase errors can be sufficiently canceled by applying the calibration of another source, which can have a large angular separation from the target (>20 deg) and significant temporal gaps. Calibrations for all-sky distributed sources with a few calibrators are also possible after FPT-square. One of the strengths and uniqueness of this calibration strategy is the suitability for high-frequency all-sky survey observations including very weak sources. We discuss the introduction of a pulse calibration system in the future to calibrate the remaining instrumental effects and allowing the possibility of imaging the source structure at high frequencies with FPT-square, where all phases are fully calibrated without involving any additional sources., Comment: 36 pages, 9 figures, published by AJ

We present multi-frequency simultaneous VLBI radio observations of the flat spectrum radio quasar 1633+382 (4C~38.41) as part of the interferometric monitoring of gamma-ray bright active galactic nuclei (iMOGABA) program combined with additional observations in radio, optical, X-rays and $\gamma-$rays carried out between the period 2012 March - 2015 August. The monitoring of this source reveals a significant long-lived increase in its activity since approximately two years in the radio bands, which correlates with a similar increase on all other bands from sub-millimeter to $\gamma-$rays. A significant correlation is also found between radio fluxes and simultaneous spectral indices during this period. The study of the discrete correlation function (DCF) indicates time lags smaller than the $\sim40$ days uncertainties among both radio bands and also high-energy bands, and a time lag of $\sim$70 days, with $\gamma-$rays leading radio. We interpret that the high-energy and radio fluxes are arising from different emitting regions, located at $1\pm12$ and $40\pm13$ pc from the central engine respectively., Comment: 16 pages, 15 figures, and 5 tables. Accepted for publication in ApJ. Small typo in the abstract corrected

The Galactic Center is the nuclear region of the nearest spiral galaxy, Milky Way, and contains the supermassive black hole with M~4x10^6 Msun, Sagittarius A* (Sgr A*). One of basic questions about the Galactic Center is whether Sgr A* alone exists as a "massive" black hole in the region or not. The IRS13E complex is a very intriguing IR object which 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 (Delta v_{FWZI} ~ 650 km/s) and a very compact size (~400 AU) in the complex using ALMA. We also found an extended component connecting with the compact ionized gas. The properties suggest that this would be an ionized gas flow on the Keplerian orbit with high eccentricity. The enclosed mass is estimated to be 10^4 Msun 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 long-term astrometry with VLBA. In addition, the object probably has an X-ray counterpart. Consequently, a very fascinated possibility is that the detected ionized gas is rotating around an IMBH embedded in the IRS13E complex., Comment: 19 pages, 4 figures, 1 table, accepted for publication in APJL

We present results of single-epoch very long baseline interferometry (VLBI) observations of gamma-ray bright active galactic nuclei (AGNs) using the Korean VLBI Network (KVN) at 22, 43, 86, and 129~GHz bands, which are part of a KVN key science program, Interferometric Monitoring of Gamma-ray Bright AGNs (iMOGABA). We selected a total of 34 radio-loud AGNs of which 30 sources are gamma-ray bright AGNs with flux densities of $>6\times10^{-10}$~ph~cm$^{-2}$~s$^{-1}$. Single-epoch multi-frequency VLBI observations of the target sources were conducted during a 24-hr session on 2013 November 19 and 20. All observed sources were detected and imaged at all frequency bands with or without a frequency phase transfer technique which enabled the imaging of 12 faint sources at 129~GHz, except for one source. Many of the target sources are resolved on milliarcsecond scales, yielding a core-jet structure with the VLBI core dominating the synchrotron emission on the milliarcsecond scale. CLEAN flux densities of the target sources are 0.43-28~Jy, 0.32-21~Jy, 0.18-11~Jy, and 0.35-8.0~Jy in the 22, 43, 86, and 129~GHz bands, respectively., Comment: 42 pages, 8 figures, 3 tables, to appear in ApJS

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., Comment: 2 pages, 1 figure, Proceedings of IAU Symposium 322 (The Multi-Messenger Astrophysics of the Galactic Centre)

We found a molecular cloud connecting from the outer region to the "Galactic Center Mini-spiral (GCMS)" which is a bundle of the ionized gas streams adjacent to Sgr A*. The molecular cloud has a filamentary appearance which is prominent in the CS J=2-1 emission line and is continuously connected with the GCMS. The velocity of the molecular cloud is also continuously connected with that of the ionized gas in the GCMS observed in the H42alpha recombination line. The morphological and kinematic relations suggest that the molecular cloud is falling from the outer region to the vicinity of Sgr A*, being disrupted by the tidal shear of Sgr A* and ionized by UV emission from the Central Cluster. We also found the SiO J=2-1 emission in the boundary area between the filamentary molecular cloud and the GCMS. There seems to exist shocked gas in the boundary area., Comment: 4 pages, 1 figure, Proceedings of IAU Symposium 322 (The Multi-Messenger Astrophysics of the Galactic Centre)

We have performed the observation of the "Galactic Center Mini-spiral(GCMS)" in H42alpha recombination line as a part of the first large-scale mosaic observation in the Sagittarius A complex using Atacama Millimeter/sub-millimeter Array (ALMA). We revealed the kinematics of the ionized gas streamers of the GCMS. We found that the ionized gas streamers of the Northern Arm(NA) and Eastern Arm(EA) in their outer regions somewhat deviate from the Keplerian orbits which were derived previously from the trajectories in the inner regions. In addition, we found that the streamer corresponding to the Bar of the GCMS has a Keplerian orbit with an eccentricity of e~0.8, which is independent from the Keplerian orbits of the other streamers of the GCMS. We estimated the LTE electron temperature and electron density in the ionized gas streamers. We confirmed the previously claimed tendency that the electron temperatures increase toward Sgr A*. We found that the electron density in the NA and EA also increases with approaching Sgr A* without the lateral expansion of the gas streamers. This suggests that there is some external pressure around the GCMS. The ambient ionized gas may cause the confinement and/or the perturbation for the orbits. There is a good positional correlation between the protostar candidates detected by JVLA at 34 GHz and the ionized gas streamer, Northeastern Arm, newly found by our H42alpha recombination line observation. This suggests that the candidates had formed in the streamer and they were brought to near Sgr A* as the streamer falls., Comment: 35 pages, 12 figures, Accepted for publication in ApJ

We present continuum images of the "Galactic Center Mini-spiral" of 100, 250, and 340 GHz bands with the analysis of the Cy.0 data acquired from the Atacama Large Millimeter/submillimeter Array (ALMA) archive. Pretty good UV coverage of the data and the "self-calibration" method give us an opportunity to obtain dynamic ranges of over 2x10^4 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 wave. The angular resolutions attain to 1.57"x1.33" in the 100 GHz band, 0.63"x0.53" in the 250 GHz band, and 0.44"x0.38" in the 340 GHz band, respectively. The continuum images clearly depict the "Mini-spiral", which is an ionized gas stream in the vicinity of Sgr A*. We found the 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 core identified by the clumpfind algorithm would obey the flat power-law dN/dM=aM^-1.5+/-0.4 on the high-mass side. These support the scenario that the star forming cloud has fallen into the immediate vicinity of Sgr A* for the origin of the Central cluster., Comment: 11 pages, 4 figures, accepted for publication in PASJ, Letter

The Interferometric Monitoring of Gamma-ray Bright Active galactic nuclei (iMOGABA) program provides not only simultaneous multifrequency observations of bright gamma-ray detected active galactic nuclei (AGN), but also covers the highest Very Large Baseline Interferometry (VLBI) frequencies ever being systematically monitored, up to 129 GHz. However, observation and imaging of weak sources at the highest observed frequencies is very challenging. In the second paper in this series, we evaluate the viability of the frequency phase transfer technique to iMOGABA in order to obtain larger coherence time at the higher frequencies of this program (86 and 129 GHz) and image additional sources that were not detected using standard techniques. We find that this method is applicable to the iMOGABA program even under non-optimal weather conditions., Comment: 19 pages, 4 tables, 10 figures, accepted for publication in JKAS

We performed a search of star-forming sites influenced by external factors, such as SNRs, HII regions, and cloud-cloud collisions, to understand the star-forming activity in the Galactic center region using the NRO Galactic Center Survey in SiO $v=0, J=2-1$, H$^{13}$CO$^+ J=1-0$, and CS $J=1-0$ emission lines obtained by the Nobeyama 45-m telescope. We found a half-shell like feature (HSF) with a high integrated line intensity ratio of $ int T_{ mathrm B}$(SiO $v=0, J=2-1$)$dv$/$ int T_{ mathrm B}$(H$^{13}$CO$^+ J=1-0$)$dv sim6-8$ in the 50 km s$^{-1}$ molecular cloud, which is a most conspicuous molecular cloud in the region and harbors an active star-forming site seen as several compact HII regions. The high ratio in the HSF indicates that the cloud contains huge shocked molecular gas. The HSF is also seen as a half-shell feature in the position-velocity diagram. A hypothesis explaining the chemical and kinetic properties of the HSF is that the feature is originated by a cloud-cloud collision (CCC). We analyzed the CS $J=1-0$ emission line data obtained by Nobeyama Millimeter Array to reveal the relation between the HSF and the molecular cloud cores in the cloud. We made a cumulative core mass function (CMF) of the molecular cloud cores within the HSF. The CMF in the CCC region is not truncated at least up to $ sim2500M_ odot$ although the CMF of the non-CCC region reaches the upper limit of $ sim1500M_ odot$. Most massive molecular cores with $M_{ mathrm{gas}}>750 M_{ odot}$ are located only around the ridge of the HSF and adjoin the compact HII region. These may be a sign of massive star formation induced by CCC in the Galactic center region., Comment: Accepted for publication in PASJ. 22 pages, 6 figures, 1 table

The Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) is the first international VLBI array dedicated to high-frequency (23 and 43 GHz bands) observations in East Asia. Here, we report the first imaging observations of three bright active galactic nuclei (AGNs) known for their complex morphologies: 4C 39.25, 3C 273, and M 87. This is one of the initial result of KaVA early science. Our KaVA images reveal extended outflows with complex substructure such as knots and limb brightening, in agreement with previous Very Long Baseline Array (VLBA) observations. Angular resolutions are better than 1.4 and 0.8 milliarcsecond at 23 GHz and 43 GHz, respectively. KaVA achieves a high dynamic range of ~1000, more than three times the value achieved by VERA. We conclude that KaVA is a powerful array with a great potential for the study of AGN outflows, at least comparable to the best existing radio interferometric arrays., Comment: 15 pages, 10 figures, 6 tables, accepted for publication in PASJ

We have carried out the first very long baseline interferometry (VLBI) imaging of 44 GHz class I methanol maser (7_{0}-6_{1}A^{+}) associated with a millimeter core MM2 in a massive star-forming region IRAS 18151-1208 with KaVA (KVN and VERA Array), which is a newly combined array of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We have succeeded in imaging compact maser features with a synthesized beam size of 2.7 milliarcseconds x 1.5 milliarcseconds (mas). These features are detected at a limited number of baselines within the length of shorter than approximately 650 km corresponding to 100 Mlambda in the uv-coverage. The central velocity and the velocity width of the 44 GHz methanol maser are consistent with those of the quiescent gas rather than the outflow traced by the SiO thermal line. The minimum component size among the maser features is ~ 5 mas x 2 mas, which corresponds to the linear size of ~ 15 AU x 6 AU assuming a distance of 3 kpc. The brightness temperatures of these features range from ~ 3.5 x 10^{8} to 1.0 x 10^{10} K, which are higher than estimated lower limit from a previous Very Large Array observation with the highest spatial resolution of ~ 50 mas. The 44 GHz class I methanol maser in IRAS 18151-1208 is found to be associated with the MM2 core, which is thought to be less evolved than another millimeter core MM1 associated with the 6.7 GHz class II methanol maser., Comment: 19 pages, 3 figures

We performed the observation of the flux densities of SgrA* at 90 and 102GHz in order to detect the 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 6 April 2005 and calculated the z-transformed discrete correlation function between the light curves. The time lag between these frequencies was not detected. If the expanding plasma model which explains the time lag at lower frequencies is valid, the light curve at 90GHz would be delayed with respect to the one at 102GHz. This result suggests that the plasma blobs ejected near the Galactic Center black hole may be widely diverse especially in optical thickness. Another possibility is that the major portion of the flux above 100GHz does not originate from the blobs., Comment: 5 pages, 5 figures, accepted for publication in PASJ

We performed the observation of the flux densities of Sgr A* at 90 and 102 GHz on 6 April 2005 using the Nobeyama Millimeter Array in order to detect the time lag between these frequencies. We constructed light curves covering a few hour with 1 min bin, and the Intra-Day Variability, which had a rising phase and intensity peak, of Sgr A* is clearly seen at both frequencies. We calculated the z-transformed discrete correlation function between the light curves of Sgr A* at 90 and 102 GHz. The derived time lag of the flares at these frequencies was approximately zero, contrary to our expectations based on the previously reported time lag at lower frequencies. If the radio flares of Sgr A* are explained by the expanding plasma model, the light curve at 90 GHz would be delayed with respect to the one at 102 GHz. However, we could not find such a delay with statistical significance in our data., Comment: 2 pages, 2 figures. Proceedings of IAU Symposium 290, "Feeding Compact Objects: Accretion on All Scales", C. M. Zhang, T. Belloni, M. Mendez & S. N. Zhang (eds.)

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 thermal equilibrium (LTE) masses of $2\times10^2-6\times10^3 M_\odot$ were identified by using the {\it 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 $dN/dM\propto M^{-2.6\pm0.1}$ ($M\gtrsim 900M_\odot$) and $dN/dR\propto R^{-5.9\pm0.3}$ ($R\gtrsim 0.35$ 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 $dN/dM\propto M^{-2.0\pm0.1}$ in the non-interacting part to $dN/dM\propto M^{-4.0\pm0.2}$ in the interacting region. On the other hand, the interaction presumably truncates the size spectrum on the larger side of $R\sim 0.4$ pc., Comment: 16 pages, 5 figures, accepted for publication in PASJ

Cygnus X-3 (Cyg X-3) is a well-known microquasar with relativistic jets. Cyg X-3 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 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 h). 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 adiabatic expanding plasma. The brightness temperature of the plasma at the peak is estimated to be $T_B\gtrsim 1 \times 10^{11}$ K. The magnetic field in the plasma is calculated to be $0.2 \lesssim H \lesssim 30$ G., Comment: 2012, PASJ 64, in press. 7 pages, 2 figures

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 millimeter wave observations of Cyg X-3 experiencing giant outbursts with one of the finest time resolutions. We find a series of short-lived flares with amplitude of 1-2 Jy in the millimeter light curve of the 2008 April-May outburst. They have flat spectra around 100 GHz. We also find abrupt and large amplitude flux density changes with e-folding time of 3.6 minutes or less. The source size of Cyg X-3 is constrained within 0.4 AU and the brightness temperature is estimated to be $T_B \gtrsim 1\times10^{11}$ K., Comment: 4 figures, PASJ, in press

We present the Australia Telescope Compact Array (ATCA) observations of the SiO masers in the Galactic center in transitions of v=1, J=2--1 at 86 GHz and v=1, J=1--0 at 43 GHz. Two 86-GHz SiO masers were detected within the central parsec, and they are associated with IRS 10EE and IRS 15NE, respectively. We detected eighteen 43-GHz SiO masers within a projected separation of <2 pc from Sagittarius A* (Sgr A*), among which seven masers are newly discovered from our observations. This raises the total number of 43-GHz SiO masers within the central 4 parsecs of the GC region to 22. Simultaneous observations at 86 and 43 GHz showed that the intensity of 43-GHz SiO maser is ~3 times higher than that of 86-GHz maser in IRS 10EE (an OH/IR star), while the integrated flux of the SiO maser emission at 43 GHz is comparable with that at 86~GHz in IRS~15NE (an ordinary Mira variable). These results are consistent with previous observations of massive late-type stars in the Galaxy in which the 86-GHz SiO maser is in general weaker than the 43-GHz SiO maser in OH/IR stars, while the two transitions are comparably strong in Mira stars., Comment: 15 pages, 3 figures, accepted by ApJ Letter

We present sensitive Australia Telescope Compact Array (ATCA) observations of SiO masers in the inner parsecs of the Galactic center (GC). We detected five SiO J=2-1, v=1 (86 GHz) masers in the innner 25 arcsec (1 pc) of the GC. All the detected 86 GHz SiO masers are previously known SiO J=1-0, v=1 (43 GHz) masers and associated with late-type stars. Eighteen 43 GHz SiO masers were detected within 50 arcsec (2 pc) of Sagittarius A*. Among them, seven are detected for the first time, which brings the total number of 43 GHz SiO masers to 22 in this region., Comment: 2 pages, 1 figure, Proceedings article for the Galactic Center Workshop 2009, Shanghai. The conference proceedings will be published in the Astronomical Society of the Pacific Conference Series

We have performed monitoring observations of the 3-mm flux density toward the Galactic Center compact radio source 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 2006 June session, and a low and variable state in 2006 August session. We report the results, with emphasis on two detected intra-day 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 can not be ignored, and a minimum mass-loss rate of 9.7*10^{-10}M_sun /yr is obtained based on parameters derived for this modified expanding plasmon model. Simultaneous multi-wavelength observation is crucial to our understanding the physical origin of rapid radio variability in Sgr A*., Comment: 25 pages, 6 figures, accepted by ApJ

We present results of multi-epoch VLBI observations with VERA (VLBI Exploration of Radio Astrometry) of the 22 GHz H$_{2}$O masers associated with a young stellar object (YSO) IRAS 22198+6336 in a dark cloud L1204G. Based on the phase-referencing VLBI astrometry, we derive an annual parallax of IRAS 22198+6336 to be 1.309$\pm$0.047 mas, corresponding to the distance of 764$\pm$27 pc from the Sun. Although the most principal error source of our astrometry is attributed to the internal structure of the maser spots, we successfully reduce the errors in the derived annual parallax by employing the position measurements for all of the 26 detected maser spots. Based on this result, we reanalyze the spectral energy distribution (SED) of IRAS 22198+6336 and find that the bolometric luminosity and total mass of IRAS 22198+6336 are 450$L_{\odot}$ and 7$M_{\odot}$, respectively. These values are consistent with an intermediate-mass YSO deeply embedded in the dense dust core, which has been proposed to be an intermediate-mass counterpart of a low-mass Class 0 source. In addition, we obtain absolute proper motions of the H$_{2}$O masers for the most blue-shifted components. We propose that the collimated jets aligned along the east-west direction are the most plausible explanation for the origin of the detected maser features., Comment: 15 pages, 7 figures, accepted for publication in PASJ (Vol.60, No.5, October 25, VERA special issue)

We have identified a weak thermal line U42.767, which has been detected only in the directions toward Sgr A and Sgr B2, as the HOCO+ 2_{02}--1_{01} transition. Because of the proximity of this line to the SiO maser line at 42.821 GHz (J=1-0 v=2),it was observable simultaneously in the ~43 GHz SiO maser searches at Nobeyama. From the past data of SiO maser surveys of infrared objects in the Galactic center, we created a map of emission distribution of HOCO+ in the Sgr A molecular cloud as well as maps of the 29SiO J=1-0 v=0 thermal emission and H53alpha emission. The emission distribution of HOCO+ was quite similar to the distribution of 29SiO emission. It suggests that the enhancement of the HOCO+ abundance in the galactic center is induced by shock activities which release the CO2 molecules frozen on grains into gases., Comment: PASJ Dec. 25, 2006 issue in press

We surveyed 291 MSX/2MASS infrared objects in the 7 x 2 deg area of the galactic center in the 43 GHz SiO J=1--0 v=1 and 2 maser lines, obtaining accurate radial velocities of 163 detected objects. The surveyed area is the region where the IRAS catalog is incomplete due to contamination by high source density. The objects in the present MSX/2MASS sample were chosen to have similar infrared characteristics to those of the previous SiO-maser-survey samples based on the color selected IRAS sources. The sampling based on the 2MASS catalog causes a bias to the foreside objects of the bulge due to heavy obscuration by interstellar dust; the detections are considerably leaned on the V_{lsr}<0 side. The l--v diagram reveals two conspicuous features, which were not present or tenuous in the previous studies: one feature indicating a linear velocity increase with longitude with |l|<1.5 deg, which is likely associated with the inner bar, and the other feature having considerably eccentric velocities more than those of the normal x_1-orbit family feature. The extinction-corrected K magnitudes (if used as a distance modulus) tend to show a sequential deposition of these objects along the line of sight toward the Galactic center depending on their radial velocities. The tendency that appeared in the distance measures is consistent with the bulge-bar dynamical model utilizing the periodic orbit families in the bar potential., Comment: Full high resolution figures available as NRO report No.638 at http://www.nro.nao.ac.jp/library/report/list.html. PASJ 58, No. 3 (June 25 issue in press)

We have performed monitoring observations of the flux density toward the Galactic center compact radio source, Sagittarius A* (Sgr A*), which is a supermassive black hole, from 1996 to 2005 using the Nobeyama Millimeter Array of the Nobeyama Radio Observatory, Japan. These monitoring observations of Sgr A* were carried out in the 3- and 2-mm (100 and 140 GHz) bands, and we have detected several flares of Sgr A*. We found intraday variation of Sgr A* in the 2000 March flare. The twofold increase timescale is estimated to be about 1.5 hr at 140 GHz. This intraday variability suggests that the physical size of the flare-emitting region is compact on a scale at or below about 12 AU (~150 Rs; Schwarzschild radius). On the other hand, clear evidence of long-term periodic variability was not found from a periodicity analysis of our current millimeter data set., Comment: 4 pages. Presented at the XXVIIIth Geleral Assembly of the URSI, Oct 2005, India