We report 4-epoch VLBA observations of 3C 66A at 22GHz. The resulting images show a typical core-jet structure. We combine our results with some previous results to investigate the proper motions of ...the jet components. The kinematics of 3C 66A is quite complicated; mildly superluminal motions as well as apparent inward motions have been detected for some components. The inward motions may imply position change of the observed core.
Results of astrometric very long baseline interferometry (VLBI) observations
towards an extreme OH/IR star candidate NSV17351 are presented. We used the
VERA (VLBI Exploration of Radio Astrometry) ...VLBI array to observe 22\,GHz
H$_2$O masers of NSV17351. We derived an annual parallax of 0.247$\pm$0.035 mas
which corresponds to a distance of 4.05$\pm$0.59 kpc. By averaging the proper
motions of 15 maser spots, we obtained the systemic proper motion of NSV17351
to be ($\mu_{\alpha}\cos{\delta}, \mu_{\delta}$)$^{\mathrm{avg}}$ $=$ ($-$1.19
$\pm$ 0.11, 1.30 $\pm$ 0.19) mas\,yr$^{-1}$. The maser spots spread out over a
region of 20 mas $\times$ 30 mas, which can be converted to a spatial
distribution of $\sim$80 au $\times$ $\sim$120 au at the source distance.
Internal motions of the maser spots suggest an outward moving maser region with
respect to the estimated position of the central star. From single dish
monitoring of the H$_2$O maser emission, we estimate the pulsation period of
NSV17351 to be 1122$\pm$24 days. This is the first report of the periodic
activity of NSV17351, indicating that NSV17351 could have a mass of
$\sim$4\,M$_{\odot}$. We confirmed that the time variation of H$_2$O masers can
be used as a period estimator of variable OH/IR stars. Furthermore, by
inspecting dozens of double-peaked H$_2$O maser spectra from the last 40 years,
we detected a long-term acceleration in the radial velocity of the
circumstellar matter to be $0.17\pm0.03$ km\,s$^{-1}$\,yr$^{-1}$ Finally, we
determined the position and kinematics of NSV17351 in the Milky Way Galaxy and
found that NSV17351 is located in an interarm region between the Outer and
Perseus arms. We note that astrometric VLBI observations towards extreme OH/IR
stars are useful samples for studies of the Galactic dynamics.
We present measurements of proper motion of the sub-parsec scale jet at 22 GHz in the nearby FR I galaxy 3C 66B. Observations were made using the VLBA at six epochs over four years. A ...phase-referencing technique was used to improve the image quality of the weak and diffuse jet components. We find that the inner knots are almost stationary, though one of them was expected to be detected with the apparent speed of 0.2 mas/yr according to 8 GHz monitoring at the same observation epochs. Clear flux variations are not observed in the core at 22 GHz, in contrast, clear flux enhancement is observed in the core at 8 GHz. We discussed that this can be explained, if the jet has helical structure, that the viewing angle of the jet between 8 and 22 GHz differs by a few degree in case the jet direction is almost along our line of sight. Although these results may imply the existence of a two-zone jet, which has been suggested in certain radio galaxies, it cannot explain the fact that the jet at the higher frequency jet is slower than that at the lower frequency.
We present proper motion of the sub-parsec scale jet in a nearby elliptical galaxy 3C 66B. Observations were made using the VLBA and partly Effelsburg 100-m telescope at 2.3 GHz and 8.4 GHz at 10 ...epochs over 4 years. The 8.4 GHz images showed that a proper motion increases from 0.21 to 0.70 mas/year, corresponding to an apparent speed of 0.30 c to 0.96 c, with a distance from the core on a sub-parsec scale. Our investigation suggests that the apparent increase of the proper motion can be explained by changes in the viewing angle, according to a relativistic beaming model. However, we still cannot eliminate the possibility that acceleration of the jet outflow speed or of changes of emissivity profile in the two-zone jet might be found in 3C 66B.
Many studies have shown that there are clear sequences in the period-luminosity relationship (PLR) for Mira variables and semiregular variables (SRVs) in the Large Magellanic Cloud (LMC). To ...investigate the PLR for SRVs in our galaxy, we examined the annual parallax measurement and conducted K'-band photometric monitoring of an SRV star SV Pegasus (SV Peg). We measured the position change of the associating H\(_2\)O maser spots by phase-referencing VLBI observations with VERA at 22 GHz, spanning approximately 3 yr, and detected an annual parallax of \(\pi = 3.00 \pm 0.06\) mas, corresponding to a distance of \(D=333 \pm 7\) pc. This result is in good agreement with the Hipparcos parallax and improves the accuracy of the distance from 35 \(\%\) to 2 \(\%\). However, the GAIA DR2 catalog gave a parallax of \(\pi=1.12\pm0.28\) mas for SV Peg. This indicates that the GAIA result might be blurred by the effect of the stellar size because the estimated stellar radius was \(\sim 5\) mas, which is comparable to the parallax. We obtained a K'-band mean magnitude of \(m_{K'} = -0.48\) mag and a period of \(P=177\) days from our photometric monitoring with a 1-m telescope. Using the trigonometric distance, we derived an absolute magnitude of \(M_{K'}=-8.09 \pm 0.05\) mag. This result shows that the position of SV Peg in the PLR falls on the C' sequence found in the PLR in the LMC, which is similar to other SRVs in our galaxy.
Results of astrometric very long baseline interferometry (VLBI) observations towards an extreme OH/IR star candidate NSV17351 are presented. We used the VERA (VLBI Exploration of Radio Astrometry) ...VLBI array to observe 22\,GHz H\(_2\)O masers of NSV17351. We derived an annual parallax of 0.247\(\pm\)0.035 mas which corresponds to a distance of 4.05\(\pm\)0.59 kpc. By averaging the proper motions of 15 maser spots, we obtained the systemic proper motion of NSV17351 to be (\(\mu_{\alpha}\cos{\delta}, \mu_{\delta}\))\(^{\mathrm{avg}}\) \(=\) (\(-\)1.19 \(\pm\) 0.11, 1.30 \(\pm\) 0.19) mas\,yr\(^{-1}\). The maser spots spread out over a region of 20 mas \(\times\) 30 mas, which can be converted to a spatial distribution of \(\sim\)80 au \(\times\) \(\sim\)120 au at the source distance. Internal motions of the maser spots suggest an outward moving maser region with respect to the estimated position of the central star. From single dish monitoring of the H\(_2\)O maser emission, we estimate the pulsation period of NSV17351 to be 1122\(\pm\)24 days. This is the first report of the periodic activity of NSV17351, indicating that NSV17351 could have a mass of \(\sim\)4\,M\(_{\odot}\). We confirmed that the time variation of H\(_2\)O masers can be used as a period estimator of variable OH/IR stars. Furthermore, by inspecting dozens of double-peaked H\(_2\)O maser spectra from the last 40 years, we detected a long-term acceleration in the radial velocity of the circumstellar matter to be \(0.17\pm0.03\) km\,s\(^{-1}\)\,yr\(^{-1}\) Finally, we determined the position and kinematics of NSV17351 in the Milky Way Galaxy and found that NSV17351 is located in an interarm region between the Outer and Perseus arms. We note that astrometric VLBI observations towards extreme OH/IR stars are useful samples for studies of the Galactic dynamics.
This paper reports the development of a gigabit real-time e-VLBI (Very Long Baseline Interferometry) geodetic system. For an experiment using the Super-Sinet of the National Institute of Informatics, ...the 32-m telescope at the Geographical Survey Institute in Tsukuba City, the National Astronomical Observatory of Japan in Mitaka City, and the 11-m telescope at Gifu University were connected using a 2.4 Gbps optical line. By two-way transmission through the optical line, S/X band data was transmitted by uplink and downlink at 2 Gbps. Their distributed correlation processing by the correlators at the National Astronomical Observatory of Japan and Gifu University realized the world's fastest real-time geodesy e-VLBI at 4 Gbps. Gaussian fitting was employed for the delay search from broadband data, enabling very accurate searches. A delay search method using phase inclination was also developed and proved to be about as accurate as the Gaussian fitting method. For the Japanese Dynamic Earth (JADE) observation by VLBI at the Geographical Survey Institute, observations by a conventional magnetic recording system (K4/K5) and the e-VLBI system were conducted simultaneously and their delays were compared. Unlike the delay of K4/K5, that of the e-VLBI was found to migrate by several hundred picoseconds a day. This is cancelled by K4/K5, which injects P-cal signals in front of the feed horn for bandwidth synthesis. However, e-VLBI may show the temperature fluctuations along the cable length between the observation room and the receiver. By baseline analysis, we could obtain geodetic results according to which this fluctuation was absorbed by clock estimation and the difference of the baseline length between K4/K5 and e-VLBI less than 3 mm.
We report multifrequency phase-referenced observations of the nearby radio galaxy NGC 4261, which has prominent two-sided jets, using the Very Long Baseline Array at 1.4-43 GHz. We measured radio ...core positions showing observing frequency dependences (known as "core shift") in both approaching jets and counter jets. The limit of the core position as the frequency approaches infinity, which suggests a jet base, is separated by 82\(\pm\)16 \({\mu}\)as upstream in projection, corresponding to (310\(\pm\)60)Rs (Rs: Schwarzschild radius) as a deprojected distance, from the 43 GHz core in the approaching jet. In addition, the innermost component at the counter jet side appeared to approach the same position at infinity of the frequency, indicating that cores on both sides are approaching the same position, suggesting a spatial coincidence with the central engine. Applying a phase referencing technique, we also obtained spectral index maps, which indicate that emission from the counter jet is affected by free-free absorption (FFA). The result of the core shift profile on the counter jet also requires FFA because the core positions at 5-15GHz cannot be explained by a simple core shift model based on synchrotron self-absorption (SSA). Our result is apparently consistent with the SSA core shift with an additional disk-like absorber over the counterjet side. Core shift and opacity profiles at the counter jet side suggest a two-component accretion: a radiatively inefficient accretion flow at the inner region and a truncated thin disk in the outer region. We proposed a possible solution about density and temperature profiles in the outer disk on the basis of the radio observation.
Recent observational results provide possible evidence that binary black holes (BBHs) exist in the center of giant galaxies and may merge to form a supermassive black hole in the process of their ...evolution. We first detected a periodic flux variation on a cycle of \(93\pm1\) days from the 3-mm monitor observations of a giant elliptical galaxy \object{3C 66B} for which an orbital motion with a period of \(1.05\pm0.03\) years had been already observed. The detected signal period being shorter than the orbital period can be explained by taking into consideration the Doppler-shifted modulation due to the orbital motion of a BBH. Assuming that the BBH has a circular orbit and that the jet axis is parallel to the binary angular momentum, our observational results demonstrate the presence of a very close BBH that has the binary orbit with an orbital period of \(1.05\pm0.03\) years, an orbital radius of \((3.9\pm1.0) \times 10^{-3}\) pc, an orbital separation of \((6.1^{+1.0}_{-0.9}) \times 10^{-3}\) pc, the larger black hole mass of \((1.2^{+0.5}_{-0.2}) \times 10^9\) \(M_{\sun}\), and the smaller black hole mass of \((7.0^{+4.7}_{-6.4}) \times 10^8\) \(M_{\sun}\). The BBH decay time of \((5.1^{+60.5}_{-2.5})\times 10^2\) years provides evidence for the occurrence of black hole mergers. This Letter will demonstrate the interesting possibility of black hole collisions to form a supermassive black hole in the process of evolution, one of the most spectacular natural phenomena in the universe.
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