275 research outputs found
Time Variation of Rotation Measure Gradient in 3C 273 Jet
The existence of a gradient in the Faraday rotation measure (RM) of the
quasar 3C 273 jet is confirmed by follow-up observations. A gradient transverse
to the jet axis is seen for more than 20 mas in projected distance. Taking
account of the viewing angle, we estimate it to be more than 100 pc. Comparing
to the distribution of the RM in 1995, we detect a time variation of it at the
same distance from the core over 7 yr. We discuss the origin of the Faraday
rotation based on this rapid time variation. We rule out foreground media such
as a narrow-line region, and suggest a helical magnetic field in the sheath
region as the origin of this gradient of the RM.Comment: 12 pages, 4 figures, published in Ap
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
Local monodromy on the fundamental groups of algebraic curves along a degenerate stable curve
VLBI observations of the most radio-loud, narrow-line quasar SDSS J094857.3+002225
We observed the narrow-line quasar SDSS J094857.3+002225, which has the
highest known radio loudness for a narrow-line Seyfert~1 galaxy (NLS1), at
1.7--15.4 GHz with the Very Long Baseline Array (VLBA). This is the first
very-long-baseline interferometry (VLBI) investigation for a radio-loud NLS1.
We independently found very high brightness temperatures from (1) its
compactness in a VLBA image and (2) flux variation among the VLBA observation,
our other observations with the VLBA, and the Very Large Array (VLA). A Doppler
factor larger than 2.7--5.5 was required to meet an intrinsic limit of
brightness temperature in the rest frame. This is evidence for highly
relativistic nonthermal jets in an NLS1. We suggest that the Doppler factor is
one of the most crucial parameters determining the radio loudness of NLS1s. The
accretion disk of SDSS J094857.3+002225 is probably in the very high state,
rather than the high/soft state, by analogy with X-ray binaries with strong
radio outbursts and superluminal jets such as GRS 1915+105.Comment: 6 pages, 2 figures, accepted for publication in PAS
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
Multifrequency Polarimetry of the Nrao 140 Jet: Possible Detection of a Helical Magnetic Field and Constraints on its Pitch Angle
We present results from multifrequency polarimetry of NRAO 140 using the Very
Long Baseline Array. These observations allow us to reveal the distributions of
both the polarization position angle and the Faraday rotation measure (RM).
These distributions are powerful tools to discern the projected and
line-of-sight components of the magnetic field, respectively. We find a
systematic gradient in the RM distribution, with its sign being opposite at
either side of the jet with respect to the jet axis. The sign of the RM changes
only with the direction of the magnetic field component along the line of
sight, so this can be explained by the existence of helical magnetic components
associated with the jet itself. We derive two constraints for the pitch angle
of the helical magnetic field from the distributions of the RM and the
projected magnetic field; the RM distribution indicates that the helical fields
are tightly wound, while that of the projected magnetic field suggests they are
loosely wound around the jet axis. This inconsistency may be explained if the
Faraday rotator is not cospatial with theemitting region. Our results may point
toward a physical picture in which an ultra-relativistic jet (spine) with a
loosely wound helical magnetic field is surrounded by a sub-relativistic wind
layer (sheath) with a tightly wound helical magnetic field.Comment: 12 pages, 4 figures, ApJ, in pres
The Analysis of the Management Control Systems in Holding Companies: Its Integrative Functions in Corporate Governance
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