1,449 research outputs found
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
The First Simultaneous 3.5 and 1.3mm Polarimetric Survey of Active Galactic Nuclei in the Northern Sky
Short millimeter observations of radio-loud AGN offer the opportunity to
study the physics of their inner relativistic jets, from where the bulk
millimeter emission is radiated. Millimeter jets are significantly less
affected by Faraday rotation and depolarization than in radio. Also, the
millimeter emission is dominated by the innermost jet regions, that are
invisible in radio owing to synchrotron opacity. We present the first dual
frequency simultaneous 86GHz and 229GHz polarimetric survey of all four Stokes
parameters of a large sample of 211 radio loud active galactic nuclei, designed
to be flux limited at 1Jy at 86GHz. The observations were most of them made in
mid August 2010 using the XPOL polarimeter on the IRAM 30 m millimeter radio
telescope. Linear polarization detections above 3 sigma median level of ~1.0%
are reported for 183 sources at 86GHz, and for 23 sources at 229GHz, where the
median 3 sigma level is ~6.0%. We show a clear excess of the linear
polarization degree detected at 229GHz with regard to that at 86GHz by a factor
of ~1.6, thus implying a progressively better ordered magnetic field for blazar
jet regions located progressively upstream in the jet. We show that the linear
polarization angle, both at 86 and 229GHz, and the jet structural position
angle for both quasars and BL Lacs do not show a clear preference to align in
either parallel or perpendicular directions. Our variability study with regard
to the 86GHz data from our previous survey points out a large degree variation
of total flux and linear polarization in time scales of years by median factors
of ~1.5 in total flux, and ~1.7 in linear polarization degree -maximum
variations by factors up to 6.3, and ~5, respectively-, with 86% of sources
showing linear polarization angles evenly distributed with regard to our
previous measurements.Comment: Submitted for Publication in Astronomy & Astrophysics. 14 pages
(including 2 tables and 18 figures
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
Synthetic synchrotron emission maps from MHD models for the jet of M87
We present self-consistent global, steady-state MHD models and synthetic
optically thin synchrotron emission maps for the jet of M87. The model consist
of two distinct zones: an inner relativistic outflow, which we identify with
the observed jet, and an outer cold disk-wind. While the former does not
self-collimate efficiently due to its high effective inertia, the latter
fulfills all the conditions for efficient collimation by the
magneto-centrifugal mechanism. Given the right balance between the effective
inertia of the inner flow and the collimation efficiency of the outer disk
wind, the relativistic flow is magnetically confined into a well collimated
beam and matches the measurements of the opening angle of M87 over several
orders of magnitude in spatial extent. The synthetic synchrotron maps reproduce
the morphological structure of the jet of M87, i.e. center-bright profiles near
the core and limb-bright profiles away from the core. At the same time, they
also show a local increase of brightness at some distance along the axis
associated to a recollimation shock in the MHD model. Its location coincides
with the position of the optical knot HST-1. In addition our best fitting model
is consistent with a number of observational constraints such as the magnetic
field in the knot HST-1, and the jet-to-counterjet brightness ratio.Comment: 9 pages, 9 figures, accepted by Ap
Anatomy of helical relativistic jets: The case of S5 0836+710
Helical structures are common in extragalactic jets. They are usually
attributed in the literature to periodical phenomena in the source (e.g.,
precession). In this work, we use VLBI data of the radio-jet in the quasar S5
0836+710 and hypothesize that the ridge-line of helical jets like this
corresponds to a pressure maximum in the jet and assume that the helically
twisted pressure maximum is the result of a helical wave pattern. For our
study, we use observations of the jet in S5 0836+710 at different frequencies
and epochs. The results show that the structures observed are physical and not
generated artificially by the observing arrays. Our hypothesis that the
observed intensity ridge-line can correspond to a helically twisted pressure
maximum is confirmed by our observational tests. This interpretation allows us
to explain jet misalignment between parsec and kiloparsec scales when the
viewing angle is small, and also brings us to the conclusion that
high-frequency observations may show only a small region of the jet flow
concentrated around the maximum pressure ridge-line observed at low
frequencies. Our work provides a potential explanation for the apparent
transversal superluminal speeds observed in several extragalactic jets by means
of transversal shift of an apparent core position with time.Comment: Accepted for publication in the Astrophysical Journa
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
La pesca en el bajo Guadalquivir Entre la tradición y el aprovechamiento de los nuevos recursos pesqueros
En número dedicado a: Sevill
- …