1,353 research outputs found
S5 0836+710: An FRII jet disrupted by the growth of a helical instability?
The remarkable stability of extragalactic jets is surprising, given the
reasonable possibility of the growth of instabilities. In addition, much work
in the literature has invoked this possibility in order to explain observed jet
structures and obtain information from these structures. For example, it was
recently shown that the observed helical structures in the jet in S5 0836+710
could be associated with helical pressure waves generated by Kelvin-Helmholtz
instability. Our aim is to resolve the arc-second structure of the jet in the
quasar S5 0836+710 and confirm the lack of a hot-spot (reverse jet-shock) found
by present observing arrays, as this lack implies a loss of jet collimation
before interaction with the intergalactic medium. In this work, we use an
observation performed in 2008 using EVN and MERLIN. The combined data reduction
has provided a complete image of the object at arc-second scales. The lack of a
hot-spot in the arc-second radio structure is taken as evidence that the jet
losses its collimation between the VLBI region and the region of interaction
with the ambient medium. This result, together with the previous identification
of the helical structures in the jet with helical pressure waves that grow in
amplitude with distance, allow us to conclude that the jet is probably
disrupted by the growth of Kelvin-Helmholtz instability. This observational
evidence confirms that the physical parameters of jets can be extracted using
the assumption that instability is present in jets and can be the reason for
many observed structures. Interestingly, the observed jet is classified as a
FRII object in terms of its luminosity, but its large-scale morphology does not
correspond to this classification. The implications of this fact are discussed.Comment: Accepted for publication in Astronomy & Astrophysic
A Global 86GHz VLBI Survey of Compact Radio Sources
We present results from a large 86GHz global VLBI survey of compact radio
sources. The main goal of the survey is to increase by factors of 3--5 the
total number of objects accessible for future 3-mm VLBI imaging. The survey
observations reach the baseline sensitivity of 0.1Jy and image sensitivity of
better than 10 mJy/beam. The total of 127 compact radio sources have been
observed. The observations have yielded images for 109 sources, extending the
database of the sources imaged at 86GHz with VLBI observation by a factor of 5,
and only 6 sources have not been detected. The remaining 12 objects have been
detected but could not be imaged due to insufficient closure phase information.
Radio galaxies are less compact than quasars and BL Lacs on sub-milliarcsecond
scale. Flux densities and sizes of core and jet components of all imaged
sources have been estimated using Gaussian model fitting. From these
measurements, brightness temperatures have been calculated, taking into account
resolution limits of the data. The cores of 70% of the imaged sources are
resolved. The core brightness temperatures of the sources peak at K and only 1% have brightness temperatures higher than K.
Cores of Intraday Variable (IDV) sources are smaller in angular size than
non-IDV sources, and so yield higher brightness temperatures.Comment: 72 pages, 12 figures, accepted for publication in the Astronomical
Journa
Simulation of Shock-Shock interaction in parsec-scale jets
The analysis of the radio light curves of the blazar CTA102 during its 2006
flare revealed a possible interaction between a standing shock wave and a
traveling one. In order to better understand this highly non-linear process, we
used a relativistic hydrodynamic code to simulate the high energy interaction
and its related emission. The calculated synchrotron emission from these
simulations showed an increase in turnover flux density, , and turnover
frequency, , during the interaction and decrease to its initial values
after the passage of the traveling shock wave.Comment: 4 pages, 1 figure, proceedings of the meeting "HEPRO III: High Energy
Phenomena in Relativistic Outflows" (Barcelona, June 2011
- …