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We successfully measured the trigonometric parallax of Sagittarius A* (Sgr A*) to be $117\pm17$ micro-arcseconds ($\mu$as) using the VLBI Exploration of Radio Astrometry (VERA) with the newly developed broad-band signal-processing system named OCTAVE-DAS. The measured parallax corresponds to a Galactocentric distance at the Sun of $R_0 = 8.5^{+1.5}_{-1.1}$ kpc. By combining the astrometric results with VERA and the Very Long Baseline Array (VLBA) over a monitoring period of 25 years, the proper motion of Sgr A* is obtained to be $(\mu_\alpha, \mu_\delta) = (-3.133\pm0.003, -5.575\pm0.005)$ mas yr$^{-1}$ in equatorial coordinates, corresponding to $(\mu_l, \mu_b) = (-6.391\pm0.005, -0.230\pm0.004)$ mas yr$^{-1}$ in Galactic coordinates. This gives an angular orbital velocity of the Sun of $\Omega_\odot = 30.30 \pm 0.02$ km s$^{-1}$ kpc$^{-1}$. We find upper limits to the core wander, $\Delta \theta < 0.20$ mas (1.6 AU), peculiar motion, $\Delta \mu < 0.10$ mas yr$^{-1}$ (3.7 km s$^{-1}$), and acceleration, $a < 2.6$ $\mu$as yr$^{-2}$ (0.10 km s$^{-1}$ yr$^{-1}$) for Sgr A*. Thus, we obtained upper mass limits of $\approx$ 3 $\times$ 10$^{4}$$M_{\odot}$ and $\approx$ 3 $\times$ 10$^{3}$$M_{\odot}$ for the supposed intermediate-mass black holes at 0.1 and 0.01 pc from the Galactic center, respectively., Comment: 15 pages, 9 figures, accepted for publication in the Publications of the Astronomical Society of Japan

We explored the parsec-scale nuclear regions of a sample of radio-loud narrow-line Seyfert 1 galaxies (NLSy1s) using the VLBI Exploration of Radio Astronomy (VERA) wideband (at a recording rate of $16\,\mathrm{Gbps}$) polarimetry at 22 and 43 GHz. Our targets include 1H 0323+342, SBS 0846+513, PMN J0948+0022, 1219+044, PKS 1502+036 and TXS 2116-077, which are all known to exhibit $\gamma$-ray emission indicative of possessing highly beamed jets similar to blazars. For the first time, we unambiguously detected Faraday rotation toward the parsec-scale radio core of NLSy1s, with a median observed core rotation measure (RM) of $2.7\times 10^3\,{\rm rad\,m^{-2}}$ (or $6.3\times 10^3\,{\rm rad\,m^{-2}}$ for redshift-corrected). This level of RM magnitude is significantly larger than those seen in the core of BL Lac objects (BLOs; a dominant subclass of blazars), suggesting that the nuclear environment of NLSy1s is more gas-rich than that in BLOs. Interestingly, the observed parsec-scale polarimetric properties of NLSy1s (low core fractional polarization, large core RM and jet-EVPA misalignment) are rather similar to those of flat-spectrum radio quasars (FSRQs). Our results are in accordance with the scenario that NLSy1s are in an early stage of AGN evolution with their central black hole masses being smaller than those of more evolved FSRQs., Comment: 22 pages, 11 figures, 7 tables. Accepted for publication in ApJ

We report on recent technical developments in the front- and back-ends for the four 20 m radio telescopes of the Japanese Very-Long-Baseline Interferometry (VLBI) project, VLBI Exploration of Radio Astrometry (VERA). We present a brief overview of a dual-circular polarization receiving and ultrawideband (16 Giga bit s$^{-1}$) recording systems that were installed on each of the four telescopes operating at 22 and 43 GHz bands. The wider-band capability improves the sensitivity of VLBI observations for continuum emission, and the dual-polarization capability enables the study of magnetic fields in relativistic jets ejected from supermassive black holes in active galactic nuclei and in sites of star formation and around evolved stars. We present the linear polarization intensity maps of extragalactic sources at 22 and 43 GHz obtained from the most recent test observations to show the state of the art of the VERA polarimetric observations. At the end of this article, given the realization of VLBI polarimetry with VERA, we describe the future prospects for scientific aims and further technical developments., Comment: 14 pages, 7 figures, 3 tables, published in the Special issue " Challenges in Understanding Black Hole Powered Jets with VLBI", Galaxies Journal

We present observational results of water vapor maser emission with our high-sensitivity 22 GHz VLBI imaging of the Seyfert galaxy NGC 1068. In this galaxy, there are the following four nuclear radio sources; NE, C, S1, and S2. Among them, the S1 component has been identified as the nucleus while the C component has been considered as attributed to the radio jet. In our VLBI observation, we find the following two types of the water maser emission at the S1 component. One is the linearly aligned component that is considered as an edge-on disk with the inner radius of 0.62 pc. The dynamical mass enclosed within the inner radius was estimated to be $1.5\times10^7 M_{\odot}$ by assuming the circular Keplerian motion. Note, however, that the best fit rotation curve shows a sub-Keplerian rotation ($v\propto r^{-0.24\pm0.10}$). The other is the water maser emission distributed around the rotating disk component up to 1.5 pc from the S1 component, suggesting the bipolar outflow from the S1 component. Further, we detected the water maser emission in the C component for the first time with VLBI, and discovered a ring-like distribution of the water maser emission. It is known that a molecular cloud is associated with the C component (both HCN and HCO$^+$ emission lines are detected by ALMA). Therefore, the ring-like maser emission can be explained by the jet collision to the molecular cloud. However, if these ring-like water masing clouds constitute a rotating ring around the C component, it is likely that the C component also has a supermassive black hole with the mass of $\sim 10^6 M_{\odot}$ that could be supplied from a past minor merger of a nucleated satellite galaxy., Comment: 16 pages, 10 figures, accepted for publication in the PASJ

We present the first astrometry catalog from the Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). We have compiled all the astrometry results from VERA, providing accurate trigonometric annual parallax and proper motion measurements. In total, 99 maser sources are listed in the VERA catalog. Among them, 21 maser sources are newly reported while the rest of 78 sources are referred to previously published results or those in preparation for forthcoming papers. The accuracy in the VERA astrometry are revisited and compared with those from the other VLBI astrometry projects such as BeSSeL (The Bar and Spiral Structure Legacy) Survey and GOBELINS (the Gould's Belt Distances Survey) with the VLBA (Very Long Baseline Array). We have confirmed that most of the astrometry results are consistent with each other, and the largest error sources are due to source structure of the maser features and their rapid variation, along with the systematic calibration errors and different analysis methods. Combined with the BeSSeL results, we estimate the up-to-date fundamental Galactic parameter of $R_{0}=7.92\pm0.16_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~kpc and $\Omega_{\odot}=30.17\pm0.27_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~km~s$^{-1}$~kpc$^{-1}$, where $R_{0}$ and $\Omega_{\odot}$ are the distance from the Sun to the Galactic center and the Sun's angular velocity of the Galactic circular rotation, respectively., Comment: 35 pages, 7 figures, accepted for publication in the Publications of the Astronomical Society of Japan

Recently a new method to discover obscured active galactic nuclei (AGNs) by utilizing X-ray and Infrared data has been developed. We carried out a survey of H2O maser emission toward ten obscured AGNs with the Nobeyama 45-m telescope. We newly detected the maser emission with the signal-noise-ratio (SNR) of above 4 from two AGNs, NGC 1402 and NGC 7738. We also found a tentative detection with its SNR > 3 in NGC 5037. The detection rate of 20% is higher than those of previous surveys (usually several percents)., Comment: 5 pages, 1 figures, 3 tables, accepted for publication in PASJ

We present survey data of the NH3 (J, K) = (1, 1)--(6, 6) lines, simultaneously observed with the Tsukuba 32-m telescope, in the main part of the central molecular zone of the Galaxy. The total number of on-source positions was 2655. The lowest three transitions were detected with S/N > 3 at 2323 positions (93% of all the on-source positions). Among 2323, the S/N of (J, K ) = (4, 4), (5, 5), and (6, 6) exceeded 3.0 at 1426 (54%), 1150 (43%), and 1359 (51%) positions, respectively. Simultaneous observations of the lines enabled us to accurately derive intensity ratios with less systematic errors. Boltzmann plots indicate there are two temperature components: cold ($\sim$ 20 K) and warm ($\sim$ 100 K). Typical intensity ratios of Tmb(2,2)/Tmb(1,1), Tmb(4,4)/Tmb(2,2), Tmb(5,5)/Tmb(4,4), and Tmb(6,6)/Tmb(3,3) were 0.71, 0.45, 0.65, and 0.17, respectively. These line ratios correspond to diversity of rotational temperature, which results from mixing of the two temperature components., Comment: 19 pages, 11 figures

We conducted a high-sensitivity radio detection survey for forty narrow-line Seyfert 1 (NLS1) galaxies using very-long-baseline interferometry (VLBI) at 22 GHz through phase-referencing long-time integration and using a newly developing recorder with a data rate of 8 Gbps, which is a candidate of the next generation VLBI data recording systems for the Japanese VLBI Network. The baseline sensitivity was typically a few mJy. The observations resulted in a detection rate of 12/40 for our radio-selected NLS1 sample; 11 out of the detected 12 NLS1s showed inverted radio spectra between 1.4 and 22 GHz on the basis of the Very Large Array flux densities and the VLBI detections. These high fractions suggest that a compact radio core with a high brightness temperature is frequently associated with NLS1 nuclei. On the other hand, at least half of the sample indicated apparently steep spectra even with the limited VLBI sensitivity. Both the inverted and steep spectrum radio sources are included in the NLS1 population., Comment: 6 pages, no figure, 1 table, accepted for publication in PASJ

We present the results of ammonia observations toward the center of NGC 3079. The NH3(J, K) = (1, 1) and (2, 2) inversion lines were detected in absorption with the Tsukuba 32-m telescope, and the NH3(1,1) through (6,6) lines with the VLA, although the profile of NH3(3,3) was in emission in contrast to the other transitions. The background continuum source, whose flux density was ~50 mJy, could not be resolved with the VLA beam of ~< 0."09 x 0."08. All ammonia absorption lines have two distinct velocity components: one is at the systemic velocity and the other is blueshifted, and both components are aligned along the nuclear jets. For the systemic components, the relatively low temperature gas is extended more than the high temperature gas. The blueshifted NH3(3,3) emission can be regarded as ammonia masers associated with shocks by strong winds probably from newly formed massive stars or supernova explosions in dense clouds in the nuclear megamaser disk. Using para-NH3(1,1), (2,2), (4,4) and (5,5) lines with VLA, we derived the rotational temperature Trot = 120 +- 12 K and 157 +- 19 K for the systemic and blueshifted components, respectively. The total column densities of NH3(0,0)-(6,6), assuming Tex ~Trot, were (8.85+-0.70) x 10^16 cm^-2 and (4.47+-0.78) x 10^16 cm-2 for the systemic and blueshifted components, respectively. The fractional abundance of NH3 relative to molecular hydrogen H2 for the systemic and blueshifted was [NH3]/[H2]=1.3x10^-7 and 6.5 x 10^-8, respectively. We also found the F = 4-4 and F = 5-5 doublet lines of OH 2{Pi}3/2 J = 9/2 in absorption, which could be fitted by two velocity components, systemic and redshifted components. The rotational temperature of OH was estimated to be Trot,OH >~ 175 K, tracing hot gas associated with the interaction of the fast nuclear outflow with dense molecular material around the nucleus., Comment: 25 pages, 9 figures, Accepted for publication in PASJ

We present analyses to determine the fundamental parameters of the Galaxy based on VLBI astrometry of 52 Galactic maser sources obtained with VERA, VLBA and EVN. We model the Galaxy's structure with a set of parameters including the Galaxy center distance R_0, the angular rotation velocity at the LSR Omega_0, mean peculiar motion of the sources with respect to Galactic rotation (U_src, V_src, W_src), rotation-curve shape index, and the V component of the Solar peculiar motions V_sun. Based on a Markov chain Monte Carlo method, we find that the Galaxy center distance is constrained at a 5% level to be R_0 = 8.05 +/- 0.45 kpc, where the error bar includes both statistical and systematic errors. We also find that the two components of the source peculiar motion U_src and W_src are fairly small compared to the Galactic rotation velocity, being U_src = 1.0 +/- 1.5 km/s and W_src = -1.4 +/- 1.2 km/s. Also, the rotation curve shape is found to be basically flat between Galacto-centric radii of 4 and 13 kpc. On the other hand, we find a linear relation between V_src and V_sun as V_src = V_sun -19 (+/- 2) km/s, suggesting that the value of V_src is fully dependent on the adopted value of V_sun. Regarding the rotation speed in the vicinity of the Sun, we also find a strong correlation between Omega_0 and V_sun. We find that the angular velocity of the Sun, Omega_sun, which is defined as Omega_sun = Omega_0 + V_sun/R_0, can be well constrained with the best estimate of Omega_sun = 31.09 +/- 0.78 km/s/kpc. This corresponds to Theta_0 = 238 +/- 14 km/s if one adopts the above value of R_0 and recent determination of V_sun ~ 12 km/s., Comment: 14 pages, 6 figures, PASJ in press

We present the results of single-dish and VLBI observations for the water-vapor masers at the nucleus of the Seyfert 2, IC 2560. We monitored velocities of the maser features with the 45-m telescope of the Nobeyama Radio Observatory. Using the data of 1995--2006, the velocity drift rate was detected to be a = +2.57 +/- 0.04 km/s/yr on the average for 6 systemic features. The Very Long Baseline Array (VLBA) with the Very Large Array (VLA) firstly detected a red-shifted and a blue-shifted maser features of IC 2560, in addition to systemic maser features and a continuum component. We propose a maser disk in the nuclear region. The systemic and red-shifted features are emitted from a nearly edge-on disk with the position angle of PA = -46 deg, which is almost perpendicular to the galactic disk. Assuming the Keplerian rotation, the radii of the maser disk are r = 0.087--0.335 pc, and the thickness is 2H <= 0.025 pc. The binding mass is 3.5 x 10^6 Msun at a distance of D = 26 Mpc, and the mean volume density within the inner radius is 1.3 x 10^9 Msun/pc^3, strongly suggesting a massive black hole at the center. A continuum component was detected at the 0.2 pc southwest of the disk center, and considered as a jet ejected from the nucleus, with an angle of 70 deg from the disk. The blue-shifted maser feature is located on the continuum component, being interpreted to be a "jet maser". The distance to IC 2560 is estimated to be D = 31^{+12}_{-14} Mpc from the geometry of the maser disk and the velocity drift rate., Comment: 17 pages, 7 figures, 5 tables, accepted for publication in PASJ

We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey (SDSS) Third Data Release, by a very-long-baseline interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network (JVN). We aimed at selecting BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversial issues of whether BAL quasars are viewed nearly edge-on, and of whether BAL quasars are in a short-lived evolutionary phase of quasar population. We detected 20 out of 22 sources using the OCTAVE baselines, implying brightness temperatures greater than 10^5 K, which presumably come from nonthermal jets. Hence, BAL outflows and nonthermal jets can be generated simultaneously in these central engines. We also found four inverted-spectrum sources, which are interpreted as Doppler-beamed, pole-on-viewed relativistic jet sources or young radio sources: single edge-on geometry cannot describe all BAL quasars. We discuss the implications of the OCTAVE observations for investigations for the orientation and evolutionary stage of BAL quasars., Comment: 10 pages, no figure, 3 tables, accepted for publication in PASJ