40 research outputs found
Binary Black Hole Accretion Flows in Merged Galactic Nuclei
We study the accretion flows from the circumbinary disks onto the
supermassive binary black holes in a subparsec scale of the galactic center,
using a smoothed particles hydrodynamics (SPH) code. Simulation models are
presented in four cases of a circular binary with equal and unequal masses, and
of an eccentric binary with equal and unequal masses. We find that the
circumblack-hole disks are formed around each black holes regardless of
simulation parameters. There are two-step mechanisms to cause an accretion flow
from the circumbinary disk onto supermassive binary black holes: First, the
tidally induced elongation of the circumbinary disk triggers mass inflow
towards two closest points on the circumbinary disk from the black holes. Then,
the gas is increasingly accumulated on these two points owing to the
gravitational attraction of black holes. Second, when the gas can pass across
the maximum loci of the effective binary potential, it starts to overflow via
their two points and freely infalls to each black hole. In circular binaries,
the gas continues to be supplied from the circumbinary disk (i.e. the gap
between the circumbinary disk and the binary black hole is always closed.) In
eccentric binaries, the mass supply undergoes the periodic on/off transitions
during one orbital period because of the variation of periodic potential. The
gap starts to close after the apastron and to open again after the next
periastron passage. Due to this gap closing/opening cycles, the mass-capture
rates are eventually strongly phase dependent. This could provide observable
diagnosis for the presence of supermassive binary black holes in merged
galactic nuclei.Comment: 16 pages, 27 figures, 2 tables, accepted for publication in PASJ.
"High Resolution Version is Available at
"http://www2.yukawa.kyoto-u.ac.jp/~kimitake/bbhs.html" Three observational
references are added. Grammatical errors and typos are correcte
Kinematics of the Radio Core in Active Galactic Nuclei(Abstracts of Doctoral Dissertations,Annual Report(from April 2002 to March 2003))
Multi-epoch, multi-frequency VLBI study of the parsec-scale jet in the blazar 3C 66A
We present the observational results of the Gamma-ray blazar, 3C 66A, at 2.3,
8.4, and 22 GHz at 4 epochs during 2004-05 with the VLBA. The resulting images
show an overall core-jet structure extending roughly to the south with two
intermediate breaks occurring in the region near the core. By model-fitting to
the visibility data, the northmost component, which is also the brightest, is
identified as the core according to its relatively flat spectrum and its
compactness. As combined with some previous results to investigate the proper
motions of the jet components, it is found the kinematics of 3C 66A is quite
complicated with components of inward and outward, subluminal and superluminal
motions all detected in the radio structure. The superluminal motions indicate
strong Doppler boosting exists in the jet. The apparent inward motions of the
innermost components last for at least 10 years and could not be caused by
new-born components. The possible reason could be non-stationarity of the core
due to opacity change.Comment: 24 pages, 4 figure
Implication of the period-magnitude relation for massive AGB stars and its astronomical applications
We present astrometric very long baseline interferometry (VLBI) studies of
AGB stars. To understand the properties and evolution of AGB stars, distances
are an important parameter. The distribution and kinematics of their
circumstellar matter are also revealed with the VLBI method. We used the VERA
array to observe 22\,GHz HO masers in various subclasses of AGB stars.
Parallaxes of the three OH/IR stars NSV17351, OH39.71.5, IRC30363, and
the Mira-type variable star AW~Tau were newly obtained. We present the
circumstellar distribution and kinematics of HO masers around NSV17351. The
absolute magnitudes in mid-infrared bands of OH/IR stars with very long
pulsation periods were investigated and a period-magnitude relation in the WISE
W3 band, , was found
for the Galactic AGB stars. The VLBI is still a powerful tool for parallax
measurements of the Galactic AGB stars surrounded by thick dust shells.Comment: 24 pages, 8 figures, Proceedings of the IAU symposium 376, At the
cross-roads of astrophysics and cosmology Period luminosity relations in the
2020
Bigradient Phase Referencing
We propose bigradient phase referencing (BPR), a new radio-observation
technique, and report its performance using the Japanese
very-long-baseline-interferometry network (JVN). In this method, a weak source
is detected by phase-referencing using a primary calibrator, in order to play a
role as a secondary calibrator for phase-referencing to a weak target. We will
be given the opportunity to select a calibrator from lots of milli-Jansky
sources, one of which may be located at the position closer to the target. With
such a smaller separation, high-quality phase-referencing can be achieved.
Furthermore, a subsequent more-sophisticated calibration can relocate array's
focus to a hypothetical point much closer to the target; a higher quality of
phase referencing is available. Our demonstrative observations with strong
radio sources have proved the capabilities of BPR in terms of image dynamic
ranges and astrometric reproducibility. The image dynamic range on a target has
been improved with a factor of about six compared to that of normal
phase-referencing; the resultant position difference of target's emission
between two epochs was only 62+-50 micro-arcsecond, even with less than 2300-km
baselines at 8.4 GHz and fast-switching of a target-calibrator pair of a
2.1-degree separation.Comment: 10 pages, 4 figures, accepted for publication in PAS
Large-Scale Regular Morphological Patterns in the Radio Jet of NGC 6251
We report on large-scale, regular morphological patterns found in the radio
jet of the nearby radio galaxy NGC 6251. Investigating morphological properties
of this radio jet from the nucleus to a radial distance of 300 arcsec
( 140 kpc) mapped at 1662 MHz and 4885 MHz by Perley, Bridle, &
Willis, we find three chains, each of which consists of five radio knots. We
also find that eight radio knots in the first two chains consist of three small
sub-knots (the triple-knotty substructures). We discuss the observational
properties of these regular morphological patterns.Comment: 8 figures, 15 pages, accepted for publication in A
High-sensitivity VLBI Observations of the Water Masers in the Seyfert Galaxy NGC 1068
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 by
assuming the circular Keplerian motion. Note, however, that the best fit
rotation curve shows a sub-Keplerian rotation ().
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 that could be supplied from a past minor merger of a nucleated
satellite galaxy.Comment: 16 pages, 10 figures, accepted for publication in the PAS