89 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
A New Test for the Absorption Mechanism of GPS Radio Sources Using Polarization Properties
We consider the use of polarization properties as a means to discriminate
between Synchrotron Self-Absorption (SSA) and Free--Free Absorption (FFA) in
GHz-Peaked Spectrum (GPS) sources. The polarization position angle (PA) of
synchrotron radiation at high frequencies for the optically thin regime is
perpendicular to the magnetic field, whereas it is parallel to the magnetic
field at low frequencies for the optically thick regime. Therefore, SSA
produces a change in PA of across the spectral peak, while FFA
does not result in such a change. We analyzed polarization data from VLA
observations for six GPS sources to see if such a change in PA was present. Our
results indicate that there is no significant evidence for change
in PA across the spectral peak, suggesting that FFA is more likely than SSA for
low-frequency cutoffs in these sources
Very Long Baseline Array Imaging of Parsec-scale Radio Emissions in Nearby Radio-quiet Narrow-line Seyfert 1 Galaxies
We conducted Very Long Baseline Array (VLBA) observations of seven nearby
narrow-line Seyfert 1 (NLS1) galaxies at 1.7 GHz (18cm) with milli-arcsecond
resolution. This is the first systematic very long baseline interferometry
(VLBI) study focusing on the central parsec-scale regions of radio-quiet NLS1s.
Five of the seven were detected at a brightness temperature of >~5x10^6 K and
contain radio cores with high brightness temperatures of >6x10^7 K, indicating
a nonthermal process driven by jet-producing central engines as is observed in
radio-loud NLS1s and other active galactic nucleus (AGN) classes. VLBA images
of MRK 1239, MRK 705, and MRK 766 exhibit parsec-scale jets with clear linear
structures. A large portion of the radio power comes from diffuse emission
components that are distributed within the nuclear regions (<~300 pc), which is
a common characteristic throughout the observed NLS1s. Jet kinetic powers
limited by the Eddington limit may be insufficient to allow the jets escape to
kiloparsec scales for these radio-quiet NLS1s with low-mass black holes of
<~10^7 M_sun.Comment: 12 pages, 3 figures, 3 tables, accepted for publication in Ap
VLBI Monitoring of 3C 84 (NGC 1275) in Early Phase of the 2005 Outburst
Multi-epoch Very Long Baseline Interferometry (VLBI) study of the sub-pc
scale jet of 3C 84 is presented. We carried out 14-epoch VLBI observations
during 2006-2009 with the Japanese VLBI Network (JVN) and the VLBI Exploration
of Radio Astrometry (VERA), immediately following the radio outburst that began
in 2005. We confirmed that the outburst was associated with the central ~1 pc
core, accompanying the emergence of a new component. This is striking evidence
of the recurrence of jet activity. The new component became brighter during
2008, in contrast to the constant gamma-ray emission that was observed with the
Fermi Gamma-ray Space Telescope during the same time. We found that the
projected speed of the new component is 0.23c from 2007/297 (2007 October 24)
to 2009/114 (2009 April 24). The direction of movement of this component
differs from that of the pre-existing component by ~40 degree. This is the
first measurement of kinematics of a sub-pc jet in a gamma-ray active phase.
Possible detection of jet deceleration and the jet kinematics in connection
with the gamma-ray emission is discussed.Comment: 5 pages, 3 figures. Accepted for publication in PAS
Ground state of the spin-1/2 chain of green dioptase at high fields
The gem-stone dioptase Cu6Si6O18.6H2O has a chiral crystal structure of
equilateral triangular helices consisting of Cu-3d spins. It shows an
antiferromagnetic order with an easy axis along c at TN = 15.5 K under zero
field, and a magnetization jump at HC = 13.5 T when the field is applied along
c-axis. By 29Si-NMR measurements, we have revealed that the high-field state is
essentially the two sub-lattice structure, and that the component within
ab-plane is collinear. The result indicates no apparent match with the
geometrical pattern of helical spin chain.Comment: SCES2013, Hongo, Toky
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