9 research outputs found
A Two-Layer Model of Venus' Atmosphere /Interpretations of Radar Observations/
Two-layer atmosphere model of Venu
Spine-sheath polarization structures in four active galactic nuclei jets
We present the results of multifrequency (15 + 8 + 5 GHz) polarization Very Long Baseline Array (VLBA) observations of the three BL Lacertae objects 0745 + 241, 1418 + 546 and 1652 + 398 together with 5-GHz VLBI Space Observatory Programme (VSOP) observations of 1418 + 546 and 1.6- and 5-GHz VSOP observations of the blazar 1055 + 018. The jets of all these sources have polarization structure transverse to the jet axis, with the polarization E vectors aligned with the jet along the jet spine and 'sheaths' of orthogonal E vectors at one or both edges of the jet. The presence of polarization aligned with the jet near the 'spine' may indicate that the jets are associated with helical B fields that propogate outward with the jet flow; the presence of orthogonal polarization near the edges of the jet may likewise be a consequence of a helical jet B field, or may be owing to an interaction with the ambient medium on parsec scales. We have tentatively detected interknot polarization in 1055 + 018 with E aligned with the local jet direction, consistent with the possibility that the jet of this source is associated with a helical B field
Multi-frequency VLBA study of the blazar S5 0716+714 during the active state in 2004: I. Inner jet kinematics
We observed the blazar \object{0716+714} with the
VLBA during its active state in 2003-2004. In this paper we discuss
multi-frequency analysis of the inner jet (first 1 mas) kinematics. The
unprecedentedly dense time sampling allows us to trace jet components without
misidentification and to calculate the component speeds with good accuracy. In
the smooth superluminal jet we were able to identify and track three components
over time moving outwards with relatively high apparent superluminal speeds
(8.5-19.4 ), which contradicts the hypothesis of a stationary oscillating
jet in this source. Component ejections occur at a relatively high rate (once
in two months), and they are accompanied by mm-continuum outbursts.
Superluminal jet components move along wiggling trajectories, which is an
indication of actual helical motion. Fast proper motion and rapid decay of the
components suggest that this source should be observed with the VLBI at a rate
of at least once in one or two months in order to trace superluminal jet
components without confusion.Comment: 4 pages, 3 figures, Astronomy & Astrophysics Letter, language
corrections adde
Multifrequency VLBA study of the blazar S5 0716+714 during the active state in 2004 II. Large-scale jet kinematics and the comparison of the different methods of VLBI data imaging as applied to kinematic studies of AGN
We study the jet kinematics of the blazar S5 0716+714 during its active state
in 2003-2004 with multi-epoch VLBI observations. Aims. We present a kinematic
analysis of the large-scale (0-12 mas) jet of 0716+714, based on the results of
six epochs of VLBA monitoring at 5 GHz. Additionally, we compare kinematic
results obtained with two imaging methods based on different deconvolution
algorithms. The blazar 0716+714 has a diffuse large-scale jet and a very faint
bright compact core. Experiments with simulated data showed that the
conventional data reduction procedure based on the CLEAN deconvolution
algorithm does not perform well in restoring this type of structure. This might
be the reason why previous kinematic studies of this source yielded ambiguous
results. In order to obtain accurate kinematics of this source, we
independently applied two imaging techniques to the raw data: the conventional
method, based on difference mapping, which uses CLEAN deconvolution, and the
generalized maximum entropy method (GMEM) realized in the VLBImager package
developed at the Pulkovo Observatory in Russia. The results of both methods
give us a consistent kinematic scenario: the large-scale jet of 0716+714 is
diffuse and stationary. Differences between the inner (0-1 mas) and outer (1-12
mas) regions of the jet in brightness and velocity of the components could be
explained by the bending of the jet, which causes the angle between the jet
direction and the line of sight to change from ~5 deg to ~11 deg. For the
source 0716+714 both methods worked at the limit of their capability.Comment: 13 pages, 7 figures. Accepted for publication in A&A, 201