455 research outputs found
Erratic Jet Wobbling in the BL Lacertae Object OJ287 Revealed by Sixteen Years of 7mm VLBA Observations
We present the results from an ultra-high-resolution 7mm Very Long Baseline
Array (VLBA) study of the relativistic jet in the BL Lacertae object OJ287 from
1995 to 2011 containing 136 total intensity images. Analysis of the image
sequence reveals a sharp jet-position-angle swing by >100 deg. during
[2004,2006], as viewed in the plane of the sky, that we interpret as the
crossing of the jet from one side of the line of sight to the other during a
softer and longer term swing of the inner jet. Modulating such long term swing,
our images also show for the first time a prominent erratic wobbling behavior
of the innermost ~0.4mas of the jet with fluctuations in position angle of up
to ~40 deg. over time scales ~2yr. This is accompanied by highly superluminal
motions along non-radial trajectories, which reflect the remarkable
non-ballistic nature of the jet plasma on these scales. The erratic nature and
short time scales of the observed behavior rules out scenarios such as binary
black hole systems, accretion disk precession, and interaction with the ambient
medium as possible origins of the phenomenon on the scales probed by our
observations, although such processes may cause longer-term modulation of the
jet direction. We propose that variable asymmetric injection of the jet flow;
perhaps related to turbulence in the accretion disk; coupled with hydrodynamic
instabilities, leads to the non-ballistic dynamics that cause the observed
non-periodic changes in the direction of the inner jet.Comment: Accepted for Publication in The Astrophysical Journal. 11 pages, 6
figures, 4 tables. High resolution images on figure 1 and complete tables 1
and 2 may be provided on reques
Unexpected High Brightness Temperature 140 PC from the Core in the Jet of 3C 120
We present 1.7, 5, 15, 22 and 43 GHz polarimetric multi-epoch VLBA
observations of the radio galaxy 3C 120. The higher frequency observations
reveal a new component, not visible before April 2007, located 80 mas from the
core (which corresponds to a deprojected distance of 140 pc), with a brightness
temperature about 600 times higher than expected at such distances. This
component (hereafter C80) is observed to remain stationary and to undergo small
changes in its brightness temperature during more than two years of
observations. A helical shocked jet model - and perhaps some flow acceleration
- may explain the unusually high Tb of C80, but it seems unlikely that this
corresponds to the usual shock that emerges from the core and travels
downstream to the location of C80. It appears that some other intrinsic process
in the jet, capable of providing a local burst in particle and/or magnetic
field energy, may be responsible for the enhanced brightness temperature
observed in C80, its sudden appearance in April 2007, and apparent
stationarity.Comment: 5 pages, 5 figures Accepted to be published in ApJ Letter
The innermost regions of the jet in NRAO 150. Wobbling or internal rotation?
NRAO 150 is a very bright millimeter to radio quasar at redshift =1.52 for
which ultra-high-resolution VLBI monitoring has revealed a counter-clockwise
jet-position-angle wobbling at an angular speed /yr in the
innermost regions of the jet. In this paper we present new total and linearly
polarized VLBA images at 43 GHz extending previous studies to cover the
evolution of the jet in NRAO 150 between 2006 and early 2009. We propose a new
scenario to explain the counter-clockwise rotation of the jet position angle
based on a helical motion of the components in a jet viewed faced-on. This
alternative scenario is compatible with the interpretation suggested in
previous works once the indetermination of the absolute position of the
self-calibrated VLBI images is taken into account. Fitting of the jet
components motion to a simple internal rotation kinematical model shows that
this scenario is a likely alternative explanation for the behavior of the
innermost regions in the jet of NRAO 150.Comment: 5 pages, 4 figures, Presented in 'The Innermost Regions of
Relativistic Jets and Their Magnetic Fields' conference. Granada, Spain, 201
3C 286: a bright, compact, stable, and highly polarized calibrator for millimeter-wavelength observations
(Context.) A number of millimeter and submillimeter facilities with linear
polarization observing capabilities have started operating during last years.
These facilities, as well as other previous millimeter telescopes and
interferometers, require bright and stable linear polarization calibrators to
calibrate new instruments and to monitor their instrumental polarization. The
current limited number of adequate calibrators implies difficulties in the
acquisition of these calibration observations. (Aims.) Looking for additional
linear polarization calibrators in the millimeter spectral range, in mid-2006
we started monitoring 3C 286, a standard and highly stable polarization
calibrator for radio observations. (Methods.) Here we present the 3 and 1 mm
monitoring observations obtained between September 2006 and January 2012 with
the XPOL polarimeter on the IRAM 30 m Millimeter Telescope. (Results.) Our
observations show that 3C 286 is a bright source of constant total flux with 3
mm flux density S_3mm = (0.91 \pm 0.02) Jy. The 3mm linear polarization degree
(p_3mm =[13.5\pm0.3]%) and polarization angle (chi_3mm
=[37.3\pm0.8]deg.,expressed in the equatorial coordinate system) are also
constant during the time span of our observations. Although with poorer time
sampling and signal-to-noise ratio, our 1 mm observations of 3C 286 are also
reproduced by a constant source of 1 mm flux density (S_1mm = [0.30 \pm 0.03]
Jy), polarization fraction (p_1mm = [14.4 \pm 1.8] %), and polarization angle
(chi_1mm = [33.1 \pm 5.7]deg.). (Conclusions.) This, together with the
previously known compact structure of 3C 286 -extended by ~3.5" in the sky-
allow us to propose 3C 286 as a new calibrator for both single dish and
interferometric polarization observations at 3 mm, and possibly at shorter
wavelengths.Comment: Accepted for publication in A&A. 7 pages, 4 figures, 8 tables.
Updated data sets with regard to previous version. New discussion about multi
frequency properties of the source. Section 3.3, Figures 3 and 4, and Tables
7 and 8 are ne
Changes in the trajectory of the radio jet in 0735+178?
We present multi-epoch 8.4 and 43 GHz Very Long Baseline Array images of the
BL Lac object 0735+178. The images confirm the presence of a twisted jet with
two sharp apparent bends of 90 within two milliarcseconds of the
core, resembling a helix in projection. The observed twisted geometry could be
the result of precession of the jet inlet, but is more likely produced by
pressure gradients in the external medium through which the jet propagates.
Quasi-stationary components are observed at the locations of the 90
bends, possibly produced by differential Doppler boosting. Identification of
components across epochs, since the earliest VLBI observations of this source
in 1979.2, proves difficult due to the sometimes large time gaps between
observations. One possible identification suggests the existence of
superluminal components following non--ballistic trajectories with velocities
up to . However, in images obtained after mid-1995,
components show a remarkable tendency to cluster near several jet positions,
suggesting a different scenario in which components have remained nearly
stationary in time at least since mid-1995. Comparison with the earlier
published data, covering more than 19 years of observations, suggests a
striking qualitative change in the jet trajectory sometime between mid-1992 and
mid-1995, with the twisted jet structure with stationary components becoming
apparent only at the later epochs. This would require a re-evaluation of the
physical parameters estimated for 0735+178, such as the observing viewing
angle, the plasma bulk Lorentz factor, and those deduced from these.Comment: 18 pages, 5 figures, accepted for publication in MNRA
On the nature of an ejection event in the jet of 3C111
We present a possible scenario for the ejection of a superluminal component
in the jet of the Broad Line Radio Galaxy 3C111 in early 1996. VLBI
observations at 15 GHz discovered the presence of two jet features on scales
smaller than one parsec. The first component evolves downstream, whereas the
second one fades out after 1 parsec. We propose the injection of a perturbation
of dense material followed by a decrease in the injection rate of material in
the jet as a plausible explanation. This scenario is supported by 1D
relativistic hydrodynamics and emission simulations. The perturbation is
modeled as an increase in the jet density, without modifying the original
Lorentz factor in the initial conditions. We show that an increase of the
Lorentz factor in the material of the perturbation fails to reproduce the
observed evolution of this flare. We are able to estimate the lifetime of the
ejection event in 3C111 to be 36\pm7 days.Comment: Accepted for publication in Astronomy & Astrophysics Letter
The milliarcsecond-scale jet of PKS 0735+178 during quiescence
We present polarimetric 5 GHz to 43 GHz VLBI observations of the BL Lacertae
object PKS 0735+178, spanning March 1996 to May 2000. Comparison with previous
and later observations suggests that the overall kinematic and structural
properties of the jet are greatly influenced by its activity. Time intervals of
enhanced activity, as reported before 1993 and after 2000 by other studies, are
followed by highly superluminal motion along a rectilinear jet. In contrast the
less active state in which we performed our observations, shows subluminal or
slow superluminal jet features propagating through a twisted jet with two sharp
bends of about 90 deg. within the innermost three-milliarcsecond jet structure.
Proper motion estimates from the data presented here allow us to constrain the
jet viewing angle to values < 9 deg., and the bulk Lorentz factor to be between
2 and 4.Comment: 11 pages, 12 figures. Accepted for publication in A&
A recollimation shock 80 mas from the core in the jet of the radio galaxy 3C120: Observational evidence and modeling
We present Very Long Baseline Array observations of the radio galaxy 3C120 at
5, 8, 12, and 15 GHz designed to study a peculiar stationary jet feature
(hereafter C80) located ~80 mas from the core, which was previously shown to
display a brightness temperature ~600 times lager than expected at such
distances. The high sensitivity of the images -- obtained between December 2009
and June 2010 -- has revealed that C80 corresponds to the eastern flux density
peak of an arc of emission (hereafter A80), downstream of which extends a large
(~20 mas in size) bubble-like structure that resembles an inverted bow shock.
The linearly polarized emission closely follows that of the total intensity in
A80, with the electric vector position angle distributed nearly perpendicular
to the arc-shaped structure. Despite the stationary nature of C80/A80,
superluminal components with speeds up to ~3 c have been detected downstream
from its position, resembling the behavior observed in the HST-1 emission
complex in M87. The total and polarized emission of the C80/A80 structure, its
lack of motion, and brightness temperature excess are best reproduced by a
model based on synchrotron emission from a conical shock with cone opening
angle \eta=10 degrees, jet viewing angle \theta=16 degrees, a completely
tangled upstream magnetic field, and upstream Lorentz factor \gamma=8.4. The
good agreement between our observations and numerical modeling leads us to
conclude that the peculiar feature associated with C80/A80 corresponds to a
conical recollimation shock in the jet of 3C120 located at a de-projected
distance of ~190 pc downstream from the nucleus.Comment: Accepted for publication in Ap
La valoración del patrimonio inmaterial en España y Japón. Una breve reflexión comparativa
El concepto de patrimonio conlleva
intrínsecamente dos valores que lo definen
y caracterizan: representatividad identitaria
del colectivo con el que se vincula (desde la
identidad étnica a las fragmentaciones socioculturales
o territoriales que la estructuran) y
capacidad de evocación de los tiempos históricos
(pasado) o modos de vida (presentes)
con los que se relaciona.
Por lo tanto, todo patrimonio se define por los
valores inmateriales que lo caracterizan, no
importa que su manifestación sea permanente
(monumento, artefacto,…) o que se active
sólo en determinados contextos.
Sea como fuere, buena parte de los valores
patrimoniales que actualmente más se enfatizan
en la cultura occidental significativamente
forman parte de las percepciones que han
caracterizado la cultura japonesa y, en general,
a las culturas “orientales”. Nos vamos
a referir a los nuevos discursos patrimonialistas
en Occidente, en concreto en España,
relacionados con los paisajes culturales y las
expresiones relacionadas con el denominado
patrimonio inmaterial. Aunque, sin embargo,
en nuestras culturas queda aún mucho por decir
sobre la percepción y significados que se
da los saberes y prácticas relacionadas con la
cultura tradicional; un campo en el que Japón
ha sido y es pionera, manifiesto en la peculiaridad
de los denominados “tesoros nacionales
vivientes” (personas portadoras de bienes
culturales intangibles importantes).The concept of heritage inherently
involves two values that define and characterize
it: identity representation of the collective
with which it is related to (from ethnic
identity to socio-cultural or territorial fragmentations),
and capacity to recall historical
periods (past) or lifestyles (present).
So heritage is defined by the intangibles values
that characterize it. It doesn’t matter if
its expressions are permanent (monuments,
artifacts,…) or they are specifically activated
in some contexts.
Anyway, a large proportion of the heritage
values that are emphasized in occidental culture
take part of perceptions which have characterized
Japanese culture and other Oriental
cultures. We will refer to new patrimonial
speeches in Occident, specifically in Spain,
which are related to cultural landscapes and
expressions of intangible heritage. However,
in Western cultures much remains to say
about the perception and meaning given to
knowledge and practises related to traditional
culture. In this area, Japan has been (and is
still being) a pioneer country, manifested in
the singularity of the called ‘living national
treasures’ (people who carry important intangible
cultural heritage)
Faraday rotation and polarization gradients in the jet of 3C~120: Interaction with the external medium and a helical magnetic field?
We present a sequence of 12 monthly polarimetric 15, 22, and 43 GHz VLBA
observations of the radio galaxy 3C 120 revealing a systematic presence of
gradients in Faraday rotation and degree of polarization across and along the
jet. The degree of polarization increases with distance from the core and
toward the jet edges, and has an asymmetric profile in which the northern side
of the jet is more highly polarized. The Faraday rotation measure is also
stratified across the jet width, with larger values for the southern side. We
find a localized region of high Faraday rotation measure superposed on this
structure between approximately 3 and 4 mas from the core, with a peak of about
6000 rad/m^2. Interaction of the jet with the external medium or a cloud would
explain the confined region of enhanced Faraday rotation, as well as the
stratification in degree of polarization and the flaring of superluminal knots
when crossing this region. The data are also consistent with a helical field in
a two-fluid jet model, consisting of an inner, emitting jet and a sheath
containing nonrelativistic electrons. However, this helical magnetic field
model cannot by itself explain the localized region of enhanced Faraday
rotation. The polarization electric vectors, predominantly perpendicular to the
jet axis once corrected for Faraday rotation, require a dominant component
parallel to the jet axis (in the frame of the emitting plasma) for the magnetic
field in the emitting region.Comment: Accepted for publication in ApJ Letters. 4 pages (including 5
figures
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