60 research outputs found
Internal Motion of 6.7-GHz Methanol Masers in H II Region S269
We present the first internal motion measurement of the 6.7-GHz methanol
maser within S269, a small HII region in the outer Galaxy, which was carried
out in 2006 and 2011 using the Japanese VLBI Network (JVN). Several maser
groups and weak isolated spots were detected in an area spanning by ~200 mas
(1000 AU). Three remarkable maser groups are aligned at a position angle of 80
degree. Two of three maser groups were also detected by a previous observation
in 1998, which allowed us to study a long-term position variation of maser
spots from 1998 to 2011. The angular separation between the two groups
increased ~10 mas, which corresponds to an expansion velocity of ~10 km s^{-1}.
Some velocity gradient (~10^{-2} km s^{-1} mas^{-1}) in the overall
distribution was found. The internal motion between the maser groups support
the hypothesis that the methanol masers in S269 could trace a bipolar outflow.Comment: 8 pages, 6 figures, accepted for publication in PAS
Very Long Baseline Interferometry imaging of H2O maser emission in the nearby radio galaxy NGC 4261
We report dual-frequency very long baseline interferometry (VLBI)
observations at 22 and 43 GHz toward the nucleus of a nearby radio galaxy NGC
4261. In particular, we present a VLBI image of the 22 GHz H2O maser line and
its location in the circumnuclear region of NGC 4261. H2O maser emission is
marginally detected above the three times the rms level within a velocity range
of approximately 2250-2450 km/s, slightly red-shifted with respect to the
systemic velocity. H2O maser emission is located approximately 1 milliarcsecond
(mas) east of the brightest continuum component at 22 GHz, where the continuum
spectrum is optically thick, that is at the free-free absorbed receding jet by
ionized gas. A positional coincidence between H2O maser emission and an ionized
gas disk implies that the H2O maser emission arises from the near side of the
disk, amplifying continuum emission from the background receding jet. If the
disk axis is oriented 64 degree relative to the line of sight, the H2O maser
emission is expected to be at a mean radius of 0.3 pc in the disk. The broad
line width of the H2O maser emission can be attributed to complex kinematics in
the immediate vicinity of the supermassive black hole (SMBH), including ongoing
gas infall onto the SMBH, turbulence, and outflow. This is analogous to the
multi-phase circumnuclear torus model in the nearest radio-loud H2O megamaser
source NGC 1052. An alternative explanation for H2O maser association is the
shock region between the jet and the ambient molecular clouds. However, this
explanation fails to describe the explicit association of H2O maser emission
only with the free-free absorbed receding jet.Comment: 10 pages, 5 figures, submitted to PAS
Short-Term Variability of PKS1510-089
We searched a short-term radio variability in an active galactic nucleus PKS
1510-089. A daily flux monitoring for 143 days at 8.4 GHz was performed, and
VLBI observations at 8.4, 22, and 43 GHz were carried out 4 times during the
flux monitoring period. As a result, variability with time scale of 20 to 30
days was detected. The variation patterns were well alike on three frequencies,
moreover those at 22 and 43 GHz were synchronized. These properties support
that this short-term variability is an intrinsic one. The Doppler factor
estimated from the variability time scale is 47. Since the Doppler factor is
not extraordinary large for AGN, such intrinsic variability with time scale
less than 30 days would exist in other AGNs.Comment: 14 pages, 4 figure
ALMA Detection of 321 GHz water maser emission in the radio galaxy NGC 1052
The Atacama Large Millimeter/submillimeter Array (ALMA) serendipitously
detected HO emission at 321 GHz in NGC
1052. This is the first submillimeter maser detection in a radio galaxy and the
most luminous 321-GHz HO maser known to date with the isotropic luminosity
of 1090 . The line profile consists of a broad velocity component
with FWHM km s straddling the systemic velocity and a
narrow component with FWHM km s blueshifted by 160 km
s. The profile is significantly different from the known 22-GHz maser which shows a broad profile redshifted by 193 km s. The
submillimeter maser is spatially unresolved with a synthesized beam of
and coincides with the
continuum core position within 12 pc. These results indicate amplification of
the continuum emission through high-temperature ( K) and dense ( cm) molecular gas in front of the coreComment: 3 figures, Accepted for publication in Publications of Astronomical
Society of Japa
Dense Plasma Torus in the GPS Galaxy NGC 1052
We report results from nearly simultaneous pentachromatic VLBI observations
towa rds a nearby GPS galaxy NGC 1052. The observations at 1.6 and 4.8 GHz with
VSOP, and at 2.3, 8.4, and 15.4 GHz wit h VLBA, provide linear resolutions of
pc. Convex spectra of a double-sided jet imply that synchrotron
emission is obscured through foreground cold dense plasma, in terms of
free--free absorption (FFA). We found a central condensation of the plasma
which covers about 0.1 pc and 1 pc of the approaching and receding jets,
respectively. A simple model with a geometrically thick plasma torus
perpendicular to the jets is established to explain the asymmetric distribution
of FFA opacities.Comment: 9 pages, 4 figures, other comment
Free-Free Absorption and the Unified Scheme
We report Very-Long-Baseline Array (VLBA) observations at 2.3, 8.4, and 15.4
GHz towards nine GHz-Peaked Spectrum (GPS) sources. One Seyfert 1 galaxy, one
Seyfert 2 galaxy, three radio galaxies, and four quasars were included in our
survey. We obtained spatial distributions of the Free-Free Absorption (FFA)
opacity with milliarcsec resolutions for all sources. It is found that type-1
(Seyfert 1 and quasars) and type-2 (Seyfert 2 and radio galaxies) sources
showed different distributions of the FFA opacities. The type-1 sources tend to
show more asymmetric opacity distributions towards a double lobe, while those
of the type-2 sources are rather symmetric. Our results imply that the
different viewing angle of the jet causes the difference of FFA opacity along
the external absorber. This idea supports the unified scheme between quasars
and radio galaxies, proposed by Barthel (1989).Comment: 17 pages, including 8 figures. Proceedings of the 3rd Compact Steep
Spectrum and GHz Peaked Spectrum Sources, 2002, Greece. Submitted to the
Publications of Astronomical Society of Australi
Annual Parallax Measurements of an Infrared Dark Cloud MSXDC G034.43+00.24 with VERA
We have measured the annual parallax of the H2O maser source associated with
an infrared dark cloud MSXDC G034.43+00.24 from the observations with VERA
(VLBI Exploration of Radio Astrometry). The parallax is 0.643 +/- 0.049 mas,
corresponding to the distance of 1.56 +0.12/-0.11 kpc. This value is less than
the half of the previous kinematic distance of 3.7 kpc. We revise the core mass
estimates of MSXDC G034.43+00.24, based on virial masses, LTE masses and dust
masses and show that the core masses decrease from the previous estimations of
~1000 Mo to hundreds of Mo. The spectral type derived from the luminosity also
changes from O9.5 to B1 in the case of MM1. This spectral type is still
consistent with that of the massive star. The radial velocity derived from the
flat rotation model is smaller than the observed velocity, which corresponds to
the peculiar motion of ~40 km/s in the line-of-sight direction.Comment: 14 pages, 11 figures, accepted to PASJ (vol. 63, No. 3
Positional Coincidence of H2O Maser and a Plasma Obscuring Torus in Radio Galaxy NGC 1052
We present multi-frequency simultaneous VLBA observations at 15, 22 and 43
GHz towards the nucleus of the nearby radio galaxy NGC 1052. These three
continuum images reveal a double-sided jet structure, whose relative intensity
ratios imply that the jet axis is oriented close to the sky plane. The steeply
rising spectra at 15-43 GHz at the inner edges of the jets strongly suggest
that synchrotron emission is absorbed by foreground thermal plasma. We detected
H2O maser emission in the velocity range of 1550-1850 km/s, which is redshifted
by 50-350 km/s with respect to the systemic velocity of NGC 1052. The
redshifted maser gas appears projected against both sides of the jet, in the
same manner as the HI seen in absorption. The H2O maser gas are located where
the free-free absorption opacity is large. This probably imply that the masers
in NGC 1052 are associated with a circumnuclear torus or disk as in the nucleus
of NGC 4258. Such circumnuclear structure can be the sence of accreting onto
the central engine.Comment: 18 pages, 7 figures, accepted for publication in Ap
VERA monitoring of the radio jet 3C 84 during 2007--2013: detection of non-linear motion
We present a kinematic study of the subparsec-scale radio jet of the radio
galaxy 3C 84/NGC 1275 with the VLBI Exploration of Radio Astrometry (VERA)
array at 22 GHz for 80 epochs from 2007 October to 2013 December. The averaged
radial velocity of the bright component "C3" with reference to the radio core
is found to be between 2007 October and 2013 December. This
constant velocity of C3 is naturally explained by the advancing motion of the
head of the mini-radio lobe. We also find a non-linear component in the motion
of C3 with respect to the radio core. We briefly discuss possible origins of
this non-linear motion.Comment: 11 pages, 7 figures, 8 tables (table 1 - 5 are supplementaries),
accepted for publication on PAS
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