Noriyuki Kawaguchi

Pilot KaVA monitoring on the M 87 jet: Confirming the inner jet structure and superluminal motions at sub-pc scales

We report the initial results of our high-cadence monitoring program on the radio jet in the active galaxy M87, obtained by the KVN and VERA Array (KaVA) at 22 GHz. This is a pilot study that preceded a larger KaVA-M87 monitoring program, which is currently ongoing. The pilot monitoring was mostly performed every two to three weeks from December 2013 to June 2014, at a recording rate of 1 Gbps, obtaining the data for a total of 10 epochs. We successfully obtained a sequence of good quality radio maps that revealed the rich structure of this jet from <~1 mas to 20 mas, corresponding to physical scales (projected) of ~0.1-2 pc (or ~140-2800 Schwarzschild radii). We detected superluminal motions at these scales, together with a trend of gradual acceleration. The first evidence for such fast motions and acceleration near the jet base were obtained from recent VLBA studies at 43 GHz, and the fact that very similar kinematics are seen at a different frequency and time with a different instrument suggests these properties are fundamental characteristics of this jet. This pilot program demonstrates that KaVA is a powerful VLBI array for studying the detailed structural evolution of the M87 jet and also other relativistic jets.

Outer rotation curve of the Galaxy with VERA. II. Annual parallax and proper motion of the star-forming region IRAS 21379+5106

We conducted astrometric VLBI observations of water-vapor maser emission in the massive star forming region IRAS 21379+5106 to measure the annual parallax and proper motion, using VERA. The annual parallax was measured to be 0.262±0.031 mas corresponding to a trigonometric distance of 3.82 −0.41 kpc. The proper motion was (μαcosδ,μδ)= (−2.74±0.08,−2.87±0.18)mas yr . Using this result, the Galactic rotational velocity was estimated to be Vθ =218±19 km s −1 at the Galactocentric distance R=9.22±0.43 kpc, when we adopted the Galactic constants R0 = 8.05± 0.45 kpc and V0 = 238± 14 km s . With newly determined distance, the bolometric luminosity of the central young stellar object was re-evaluated to (2.15± 0.54)× 10L⊙, which corresponds to spectral type of B2–B3. Maser features were found to be distributed along a straight line from south-west to north-east. In addition, a vector map of the internal motions constructed from the residual proper motions implies that maser features trace a bipolar flow and that it cannot be explained by simple ballistic motion.

VLBI Imaging of M81∗ at λ = 3.4 mm with Source-frequency Phase-referencing

We report on the first VLBI image of the M81 nucleus (M81∗) at a wavelength of 3.4 mm, obtained with the source-frequency phase-referencing (SFPR) technique. Thanks to the SFPR calibration, the coherent integration time eventually could be increased by more than an order of magnitude, which enabled the detection of fringes at the level of 45 mJy beam -1 with a dynamic range higher than 130:1. This paves the way toward future millimeter/submillimeter VLBI observations of weaker sources. From the analysis of the M81∗ visibilities, a core size of ∼50 μas at 3.4 mm was estimated. This follows the power-law relationship with wavelength, , reported previously at lower frequencies. These results constrain the core size (at 3.4 mm) to a minimum of ∼80 Schwarzschild radii of M81∗.

Millimeter VLBI observations of Sgr A* with KaVA and KVN

We present recent observation results of Sgr A* at millimeter obtained with VLBI arrays in Korea and Japan. 7 mm monitoring of Sgr A* is part of our AGN large project. The results at 7 epochs during 2013-2014, including high resolution maps, flux density and two-dimensional size measurements are presented. The source shows no significant variation in flux and structure related to the G2 encounter in 2014. According to recent MHD simulations by kawashima et al., flux and magnetic field energy can be expected to increase several years after the encounter; We will keep our monitoring in order to test this prediction. Astrometric observations of Sgr A* were performed in 2015 at 7 and 3.5 millimeter simultaneously. Source-frequency phase referencing was applied and a combined ”core-shift” of Sgr A* and a nearby calibrator was measured. Future observations and analysis are necessary to determine the core-shift in each source.

New observing system of the 45-m telescope at Nobeyama Radio Observatory

We developed a new observing system to improve the performance of the 45-m telescope at Nobeyama Radio Observatory (NRO). The system consists of new receivers, new IF converters, new A/D converters, and a new spectrometer. The technologies developed for ALMA (the Atacama Large Millimeter/Submillimeter Array) were used for many parts (e.g., receivers and spectrometers). With the new system, we are conducting surveys of distant primeval galaxies and line surveys of various targets.

A VLBI Study of H2O Maser Spots Associated with a Molecular Outflow ρ Oph-East

A molecular outflow is one of the most conspicuous active phenomena associated with protostars, and the kinetic energy of its outflowing mass is as large as that of random motions of ambient molecular cloud, which suggests that outflow has dynamically influence on ambient molecular gas. Possible observational evidence which suggests the existence of dynamical interaction between molecular outflow and ambient molecular cloud has been detected in several star forming regions (Fukui et al. 1986; Iwata et al. 1988). Recent detections of H 2 O maser emission associated with low-mass protostars (e.g. Comoretto et al. 1990) also suggest that there still exist active phenomena in the low-mass star forming regions. Molecular outflow ρ Oph-East, discovered toward a low-mass protostar IRAS 16293-2422 (Fukui et al. 1986), has been known as a site of dynamical interaction between molecular outflowing gas and ambient molecular cloud by CO and NH 3 observation (Mizuno et al. 1990). Existence of several strong H 2 O maser spots (Wilking & Claussen 1987; Wotten 1989; Terebey et al. 1992) also suggests that active phenomena are occurring in this region. In this paper, we report our result of H 2 O maser observation for molecular outflow ρ Oph-East with milli-arcsecond resolution by VLBI.

The CRL 34-m radio telescope at Kashima — A new strong tool in maser research — and the first results of a 22 GHz H2O maser survey

The CRL 34-m radio telescope at Kashima was completed in 1988. The telescope is equipped with low noise receivers from 1.4 GHz to 44 GHz and is able to observe most of the important astronomical masers in this frequency range. We made an automatic maser survey software and started an H20 maser survey at November 1991 for IRAS color selected objects. Until the end of January 1992, about 930 sources were observed with the rms noise level of 0.1 Jy and about 300 sources were detected.