417 research outputs found
The non-ballistic superluminal motion in the plane of the sky-II
The model of non-ballistic jet motion proposed in 2008 provides a simple
explanation to the inward jet motion and bent jet. Recently, evidences of such
a non-radial motion increase rapidly, and more complicated morphologies appear.
On the other hand, the ballistic plus precession model likely holds in majority
samples of jet motion. This paper discusses the relationship between the
ballistic and non-ballistic model of jet motion, which suggests that the
interaction of ejectors with ambient matter can produce knots at different
stages of evolution and hence different separations to the core. And as a jet
precesses, knots produced between the core and the deceleration radius result
in spiral pattern expected by the model of ballistic plus precession; and knots
generated at the deceleration radius display non-radial motion such as bent jet
or oscillation of ridge-line. This paper develops the first non-ballistic model
in four aspects. Firstly, it provides a numerical simulation to the production
of multi-knot for a precessing jet. Secondly, it fits the precession behavior
of multi-knot and interprets the oscillation of ridge lines like S5 1803+784.
Thirdly, it gives an unified interpretation to the bent jet applicable to both
multi-knot and single knot. And fourthly, the problem of very large numbers of
observed outward motions as opposed to the inward ones is addressed in a new
scope.Comment: 9 pages, 6 figures, accepted by MNRA
Deconstructing blazars: A different scheme for jet kinematics in flat-spectrum AGN
Recent VLBI studies of the morphology and kinematics of individual BL Lac
objects (S5 1803+784, PKS 0735+178, etc.) have revealed a new paradigm for the
pc-scale jet kinematics of these sources. Unlike the apparent superluminal
outward motions usually observed in blazars, most, if not all, jet components
in these sources appear to be stationary with respect to the core, while
exhibiting strong changes in their position angles. As a result, the jet ridge
lines of these sources evolve substantially, at times forming a wide
channel-flow. We investigate the Caltech-Jodrell Bank flat-spectrum (CJF)
sample of radio-loud active galaxies to study this new kinematic scenario for
flat-spectrum AGN. We develop a number of tools that extract information about
the apparent linear and angular evolution of the CJF jet ridge lines, as well
as their morphology. In this way, we study both radial and non-radial apparent
motions in the CJF jets. We find that approximately half of the sample shows
appreciable apparent jet widths (), with BL Lac jet ridge lines
showing significantly larger apparent widths than both quasars and radio
galaxies. In addition, BL Lac jet ridge lines are found to change their
apparent width more strongly. Finally, BL Lac jet ridge lines show the least
apparent linear evolution, which translates to the smallest apparent expansion
speeds for their components. We find compelling evidence supporting a
substantially different kinematic scenario for flat-spectrum radio-AGN jets and
in particular for BL Lac objects. In addition, we find that variability is
closely related to the properties of a source's jet ridge line. Variable
quasars are found to show "BL Lac like" behavior, compared to their
non-variable counterparts.Comment: 16 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
Understanding BL Lac objects Structural & kinematic mode changes in the BL Lac object PKS 0735+178
Context. We present evidence that parsec-scale jets in BL Lac objects may be
significantly distinct in kinematics from their counterparts in quasars. We
argued this previously for the BL lac sources 1803+784 and 0716+714, report
here a similar pattern for another well-known BL Lac object, PKS 0735+178,
whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. A
detailed study of the jet components' motion reveals that the standard AGN
paradigm of apparent superluminal motion does not always describe the
kinematics in BL Lac objects. We study 0735+178 here to augment and improve the
understanding of the peculiar motions in the jets of BL Lac objects as a class.
Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations
(2cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91.
Results. We found a drastic structural mode change in the VLBI jet of 0735+178,
between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a
linear shape.We further found that this jet had undergone a similar transition
sometime between December 1981 and June 1983. A mode change, occurring in the
reverse direction (between mid-1992 and mid-1995) has already been reported in
the literature. These structural mode changes are found to be reflected in
changed kinematical behavior of the nuclear jet, manifested as an apparent
superluminal motion and stationarity of the radio knots. In addition, we found
the individual mode changes to correlate in time with the maxima in the optical
light curve. The last two transitions occurred before a (modest) radio flare.
The behavior of this pc-scale jet appears to favor a scenario involving
non-ballistic motions of the radio knots, produced by the precession of a
continuous jet within the ambient medium.Comment: Accepted for publication in A&A (Abstract reduced for astro-ph
Constraining the parameters of the putative supermassive binary black hole in PG 1302-102 from its radio structure
We investigate the pc-scale kinematics and kpc-scale radio morphology of the
quasar PG 1302-102, which may harbour a sub-pc separation supermassive binary
black hole system at its centre as inferred from optical variability.
High-resolution radio interferometric measurements obtained with the Very Long
Baseline Array (VLBA) in the Monitoring Of Jets in Active galactic nuclei with
VLBA Experiments (MOJAVE) programme at 15 GHz at 20 epochs spanning 17 years
were analysed to investigate the pc-scale radio structure. Archival
observations with the Very Large Array (VLA) at 1.4 GHz and 5 GHz were obtained
to study the kpc-scale morphology. We find that the pc-scale jet is inclined
within ~2.2 deg to the line of sight and has a half-opening angle of about 0.2
deg. The parameters derived from the pc-scale radio jet are qualitatively
consistent with those obtained from the analysis of the optical light curve of
PG 1302-102. We obtain at least 0.08 for the mass ratio of the two black holes
in the system. We find some indication for a helical jet structure on
kpc-scale, but the directions of the inner and the extended radio jets are
significantly different, obstructing a straightforward connection of the pc-
and kpc-scale jets within the binary scenario.Comment: 9 pages, 4 figures, 1 table, accepted to MNRA
Is 0716+714 a superluminal blazar?
We present an analysis of new and old high frequency VLBI data collected
during the last 10 years at 5--22 GHz. For the jet components in the mas-VLBI
jet, two component identifications are possible. One of them with
quasi-stationary components oscillating about their mean positions. Another
identification scheme, which formally gives the better expansion fit, yields
motion with for km s Mpc and .
This model would be in better agreement with the observed rapid IDV and the
expected high Lorentz-factor, deduced from IDV.Comment: 2 pages, 3 figures, appears in: Proceedings of the 6th European VLBI
Network Symposium held on June 25th-28th in Bonn, Germany. Edited by: E. Ros,
R.W. Porcas, A.P. Lobanov, and J.A. Zensu
High resolution observations of Cen A: Yellow and red supergiants in a region of jet-induced star formation?
We present the analysis of near infrared (NIR), adaptive optics (AO) Subaru
and archived HST imaging data of a region near the northern middle lobe (NML)
of the Centaurus A (Cen A) jet, at a distance of kpc north-east (NE)
from the center of NGC5128. Low-pass filtering of the NIR images reveals strong
-- above the background mean -- signal at the expected position of
the brightest star in the equivalent HST field. Statistical analysis of the NIR
background noise suggests that the probability to observe signal at
the same position, in three independent measurements due to stochastic
background fluctuations alone is negligible () and, therefore,
that this signal should reflect the detection of the NIR counterparts of the
brightest HST star. An extensive photometric analysis of this star yields
, visual-NIR, and NIR colors expected from a yellow supergiant (YSG) with
an estimated age Myr. Furthermore, the second and third
brighter HST stars are, likely, also supergiants in Cen A, with estimated ages
Myr and Myr, respectively. The ages of
these three supergiants are in good agreement with the ages of the young
massive stars that were previously found in the vicinity and are thought to
have formed during the later phases of the jet-HI cloud interaction that
appears to drive the star formation (SF) in the region for the past
Myr.Comment: 11 pages, 6 figures, 2 tables, accepted for publication in Ap
The kinematics in the pc-scale jets of AGN The case of S5 1803+784
We present a kinematic analysis of jet component motion in the VLBI jet of
the BL Lac object S5 1803+784, which does not reveal long-term outward motion
for most of the components. Understanding the complex kinematic phenomena can
possibly provide insights into the differences between quasars and BL Lac
objects. The blazar S5 1803+784 has been studied with VLBI at =1.6, 2.3,
5, 8.4, and 15 GHz between 1993.88 and 2005.68 in 26 observing runs. We
(re)analyzed the data and present Gaussian model-fits. We collected the already
published kinematic information for this source from the literature and
re-identified the components according to the new scenario presented in this
paper. Altogether, 94 epochs of observations have been investigated. A careful
study of the long-term kinematics reveals a new picture for component motion in
S5 1803+784. In contrast to previously discussed motion scenarios, we find that
the jet structure within 12 mas of the core can most easily be described by the
coexistence of several bright jet features that remain on the long-term at
roughly constant core separations (in addition to the already known {\it
stationary} jet component 1.4 mas) and one faint component moving with
an apparent superluminal speed ( 19c, based on 3 epochs). While most of
the components maintain long-term roughly constant distances from the core, we
observe significant, smooth changes in their position angles. We report on an
evolution of the whole jet ridge line with time over the almost 12 years of
observations. The width of the jet changes periodically with a period of
8 to 9 years. We find a correlation between changes in the position angle and
maxima in the total flux-density. We present evidence for a geometric origin of
the phenomena and discuss possible models.Comment: The manuscript will be published by A&
SUBARU and e-Merlin observations of NGC3718. Diaries of an SMBH recoil?
NGC3718 is a LINER galaxy, lying at a distance of about
Mpc away from earth and its similarities with NGC5128 often award it the name
"northern Centaurus A". We use high angular resolution ( mas) e-Merlin
radio and SUBARU NIR ( mas) data, to take a detailed view of the
processes taking place in its central region. In order to preserve some
objectivity in our interpretation, we combine our results with literature
values and findings from previous studies. Our NIR maps suggest, on one hand,
that towards the stellar bulge there are no large scale absorption phenomena
caused by the apparent dust lane and, on the other, that there is a significant
(local) contribution from hot ( K) dust to the nuclear NIR emission.
The position where this takes place appears to be closer to the offset compact
radio emission from our e-Merlin cm map, lying offset by pc from
the center of the underlying stellar bulge. The shape of the radio map suggests
the presence of one (or possibly two, forming an X-shape) bipolar structure(s)
() arcsec across, which combined with the balance between the
gas and the stellar velocity dispersions and the presence of hard X-ray
emission, point towards effects expected by AGN feedback. We also argue that
NGC3718 has a "core" in its surface brightness profile, despite the fact that
it is a gas-rich galaxy and we discuss its mixed photometric and spectroscopic
characteristics. The latter combined with the observed spatial and radio
offsets, the relative redshift between the broad and the narrow
line, the limited star formation activity and AGN
feedback, strongly imply the existence of an SMBH recoil. Finally, we discuss a
possible interpretation, that could naturally incorporate all these findings
into one physically consistent picture.Comment: 18 pages, 18 figures, 3 tables, accepted for publications in A&
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