Kazuhiro Hada

An origin of the radio jet in M87 at the location of the central black hole

Powerful radio jets from active galactic nuclei are thought to be powered by the accretion of material onto the supermassive black hole (the ‘central engine’). M87 is one of the closest examples of this phenomenon, and the structure of its jet has been probed on a scale of about 100 Schwarzschild radii (Rs, the radius of the event horizon). However, the location of the central black hole relative to the jet base (a bright compact radio ‘core’) remains elusive. Observations of other jets indicate that the central engines are located about 104–106Rs upstream from the radio core. Here we report radio observations of M87 at six frequencies that allow us to achieve a positional accuracy of about 20 microarcseconds. As the jet base becomes more transparent at higher frequencies, the multifrequency position measurements of the radio core enable us to determine the upstream end of the jet. The data reveal that the central engine of M87 is located within 14–23Rs of the radio core at 43 GHz. This implies that the site of material infall onto the black hole and the eventual origin of the jet reside in the bright compact region seen on the image at 43 GHz.

The kinematic of HST-1 in the jet of M 87

Aims. We aim to constrain the structural variations within the HST-1 region downstream of the radio jet of M87, in general as well as in connection to the episodes of activity at very high energy (VHE). Methods. We analyzed and compared 26 VLBI observations of the M87 jet, obtained between 2006 and 2011 with the Very Long Baseline Array (VLBA) at 1.7 GHz and the European VLBI Network (EVN) at 5 GHz. Results. HST-1 is detected at all epochs; we model-fitted its complex structure with two or more components, the two outermost of which display a significant proper motion with a superluminal velocity around ∼4c. The motion of a third feature that is detected upstream is more difficult to characterize. The overall position angle of HST-1 has changed during the time of our observations from −65 ◦ to −90 ◦ , while the structure has moved by over 80 mas downstream. Our results on the component evolution suggest that structural changes at the upstream edge of HST-1 can be related to the VHE events.

SUZAKU OBSERVATION OF THE GIANT RADIO GALAXY 3C 326

A Suzaku observation of a giant radio galaxy, 3C 326, which has a physical size of about 2 Mpc, was conducted on 2008 January 19-21. In addition to several X-ray sources, diffuse emission was significantly detected and associated with its west lobe, but the east lobe was contaminated by an unidentified X-ray source WARP J1552.4+2007. After careful evaluation of the X-ray and non-X-ray background, the 0.4-7 keV X-ray spectrum of the west lobe is described by a power-law model modified with the Galactic absorption. The photon index and 1 keV flux density were derived as Γ = 1.82+0.26 –0.24 ± 0.04 and S X = 19.4+3.3 –3.2 ± 3.0 nJy, respectively, where the first and second errors represent the statistical and systematic ones. The diffuse X-rays were attributed to be inverse Compton (IC) radiation by the synchrotron radio electrons scattering off the cosmic microwave background photons. This radio galaxy is the largest among those with lobes detected through IC X-ray emission. A comparison of the radio to X-ray fluxes yields the energy densities of electron and magnetic field as ue = (2.3 ± 0.3 ± 0.3) × 10–13 erg cm–3 and um = (1.2+0.2 –0.1 ± 0.2) × 10–14 erg cm–3, respectively. The galaxy is suggested to host a low-luminosity nucleus with an absorption-corrected 2-10 keV luminosity of <2 × 1042 erg s–1, together with a relatively weak radio core. The energetics in the west lobe of 3C 326 were compared with those of moderate radio galaxies with a size of ~100 kpc. The west lobe of 3C 326 is confirmed to agree with the correlations for the moderate radio galaxies, ue ∝ D –2.2 ± 0.4 and um ∝ D –2.4 ± 0.4, where D is their total physical size. This implies that the lobes of 3C 326 are still being energized by the jet, despite the current weakness of the nuclear activity.

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.

A wide and collimated radio jet in 3C84 on the scale of a few hundred gravitational radii

Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem1. This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very-long-baseline interferometry that has thus far been able to probe the structure of the jet acceleration and collimation region in only two sources2,3. Here, we report observations of 3C84 (NGC 1275)—the central galaxy of the Perseus cluster—made with an interferometric array including the orbiting radio telescope of the RadioAstron4 mission. The data transversely resolve the edge-brightened jet in 3C84 only 30 μas from the core, which is ten times closer to the central engine than was possible in previous ground-based observations5 and allows us to measure the jet collimation profile from ~102 to ~104 gravitational radii (rg) from the black hole. The previously found5, almost cylindrical jet profile on scales larger than a few thousand rg is seen to continue at least down to a few hundred rg from the black hole, and we find a broad jet with a transverse radius of ≳250 rg at only 350 rg from the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales ≲102 rg or it is launched from the accretion disk.Interferometric observations of 3C84 reveal a broad cylindrical jet a few hundred gravitational radii from the black hole, implying that the jet either undergoes a rapid lateral expansion on even smaller scales or is launched from the accretion disk.

Evidence of Jet–Clump Interaction: A Flip of the Radio Jet Head of 3C 84

Radio jets in active galaxies have been expected to interact with circumnuclear environments in their early phase evolutions. By performing the multi-epoch monitoring observation with the KVN and VERA Array (KaVA) at 43~GHz, we investigate the kinematics of the notable newborn bright component C3 located at the tip of the recurrent jet of 3C~84. During 2015 August-September, we discover the flip of C3 and the amount of the flip is about 0.4~milli-arcsecond in angular scale, which corresponds to 0.14 parsec in physical scale. After the flip of C3, it wobbled at the same location for a few months and then it restarted to propagate towards the southern direction. The flux density of C3 coherently showed the monotonic increase during the observation period. The flip is in good agreement with hydrodynamical simulations of jets in clumpy ambient medium. We estimate the number density of the putative clump based on the momentum balance between the jet thrust and the ram pressure from the clump and it is about

Water vapor megamasers in a circumnuclear ionized torus in the Seyfert galaxy Mrk 348

10^{3-5}~{\rm cm^{-3}}

The structure of the circumnuclear absorber in NGC 4261 by multi-frequency phase-referencing observation

. We briefly discuss possible origins of the clump.

Collimation, Acceleration, and Recollimation Shock in the Jet of Gamma-Ray Emitting Radio-loud Narrow-line Seyfert 1 Galaxy 1H0323+342

We conducted phase-referenced VLBA observations at 1.7–22 GHz for the type-2 Seyfert galaxy Mrk 348 (D = 62 Mpc) which has water vapor megamasers of very broad line width (∼ 100 km s−1). The physical origin of the broad-line masers has been debated. We investigated (1) the position-velocity distribution of the masers, (2) a frequency-dependent core shift, and (3) the opacity distribution of free-free absorption in the nuclear region of Mrk 348. In this paper, we report some observational results. The details of the maser velocity field (with infall and rotation), the enclosed mass and the location of the dynamical center, and the structure of the circumnuclear ionized torus will be presented in another paper.

VERA monitoring of the radio jet 3C 84 in the period of 2007–2013: Detection of non-linear motion

Takafumi Haga∗†,1 Akhiro Doi,2 Yasuhiro Murata,2 Hiroshi Sudo,3 Seiji Kameno,4 and Kazuhiro Hada5 1 Department of Space and Astronautical Science, The Graduate University for Advanced Studies (SOKENDAI) 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan 2 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan 3 Department of Mathematical and Design Engineering, Faculty of Engineering, Gifu University 1-1 Yanagido, Gifu City 501-1193, Japan 4 Department of Physics, Faculty of Science, Kagoshima University 1-21-24, Korimoto, Kagoshima 890-8580, Japan 5 INAF Istituto di Radioastronomia via Gobetti 101, 40129 Bologna Italy