1,812 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
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
An infrared study of galactic OH/IR stars. I. An optical/near-IR atlas of the Arecibo sample
In this paper we present optical and near-infrared finding charts, accurate
astrometry (~1") and single-epoch near-infrared photometry for 371 IRAS
sources, 96% of those included in the so-called Arecibo sample of OH/IR stars
(Eder et al. 1988; Lewis et al. 1990a; Chengalur et al. 1993). The main
photometric properties of the stars in the sample are presented and discussed
as well as the problems found during the process of identification of the
optical/near-infrared counterparts. In addition, we also identify suitable
reference stars in each field to be used for differential photometry purposes
in the future.
We find that 39% of the sources (144 in number) have no optical counterpart,
8 of them being invisible even at near infrared wavelengths. The relative
distribution of sources with and without optical counterpart in the IRAS
two-colour diagram and their characteristic near infrared colours are
interpreted as the consequence of the increasing thickness of their
circumstellar shells. Among the objects not detected at near infrared
wavelengths four non-variable sources are proposed to be heavily obscured
post-AGB stars which have just very recently left the AGB. Eight additional
objects with unusually bright and/or blue near-infrared colours are identified
as candidate post-AGB stars and/or proto-planetary nebulae.Comment: 28 pages, 9 figures, for associated finding charts see:
http://www.edpsciences.org/articles/aa/full/2005/08/aa1709/FINDING_CHARTS/are
cibo_index.htm
Monthly 43 GHz VLBA Polarimetric Monitoring of 3C120 over 16 Epochs: Evidence for Trailing Shocks in a Relativistic Jet
We present a 16-month sequence of monthly polarimetric 43 GHz VLBA images of
the radio galaxy 3C 120. The images probe the inner regions of the radio jet of
this relatively nearby superluminal radio galaxy at a linear resolution of 0.07
pc ( km s Mpc). We follow the
motion of a number of features with apparent velocities between 4.010.08
and . A new superluminal knot, moving at , is observed to be ejected from the core at a time
coincident with the largest flare ever observed for this source at millimeter
wavelengths. Changes in the position angle of this component, as well as a
progressive rotation of its magnetic polarization vector, suggest the presence
of a twisted (resembling a helix in projection) configuration of the underlying
jet magnetic field and jet geometry. We identify several knots that appear in
the wake of the new superluminal component, moving at proper motions
times slower than any of the other moving knots observed in 3C 120. These
features have properties similar to those of the ``trailing'' shocks seen in
relativistic, time-dependent, hydrodynamical and emission simulations of
compact jets. Such trailing compressions are triggered by pinch-mode jet-body
instabilities caused by the propagation of a strong perturbation, which we
associate with the new strong superluminal component.Comment: 4 pages, 5 figures, accepted for publication in Astrophysical Journal
Letter
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