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تسجيل مستخدم جديدAn extremely curved relativistic jet in PKS 2136+141
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T. Savolainen
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We report the discovery of an extremely curved jet in the high frequency peaking GPS quasar PKS 2136+141. Our multi-frequency VLBA images show a bending jet making a turn-around of 210 degrees on the plane of the sky, which is, to our knowledge, the largest ever observed change in a structural position angle of an extragalactic jet. Images taken at six different frequencies, from 2 to 43 GHz, beautifully reveal a spiral-like trajectory. We discuss possibilities to constrain the 3-D geometry of the source and suggest that it could be used as a testbed for models describing the bending of the relativistic jets.
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We report the discovery of an extremely curved jet in the radio-loud quasar PKS2136+141. Multi-frequency Very Long Baseline Array (VLBA) images show a bending jet making a turn-around of 210 degrees in the plane of the sky, which is, to our knowledge
, the largest ever observed change in the position angle of an astrophysical jet. Images taken at six different frequencies, from 2.3 to 43 GHz, reveal a spiral-like trajectory, which is likely a sign of an intrinsic helical geometry. A space-VLBI image, taken with the HALCA satellite at 5 GHz and having comparable resolution to our ground-based 15 GHz data, confirms that the bend is a frequency-independent structure. VLBA monitoring data at 15 GHz, covering eight years of observations, show knots in the jet clearly deviating from ballistic motion, which suggests that the bending may be caused by a growing helical Kelvin-Helmholtz normal mode. The jet appearance suggests a helical wave at a frequency well below the resonant frequency of the jet, which indicates that the wave is driven by a periodic perturbation at the base of the jet. We fit the observed structure in the source with a helical twist, and we find that a simple isothermal model with a constant wave speed and wavelength gives a good fit. The measured apparent velocities indicate some degree of acceleration along the jet, which together with an observed change in the apparent half-opening angle of the jet allow us to estimate the changes in the angle between the local jet direction and our line of sight. We suggest that the jet in PKS2136+141 is distorted by a helical Kelvin-Helmholtz normal mode externally driven into the jet (e.g. by precession), and that our line of sight falls within the opening angle of the helix cone.
We carried out a multifrequency and multiepoch study of the highly polarized quasar, PKS 1502+106 at radio frequencies. The analysis is based on an EVN dataset at 5 GHz, archive VLBA datasets at 2.3, 8.3, 24.4 and 43.1 GHz and an archive MERLIN datas
et at 5 GHz. The various datasets span over a period of 10 years. The source is characterized by a multi-component one-sided jet at all epochs. The VLBI images show that a complex curved jet is located to the southeast and east of the core, with the position angle (PA) of the jet axis wiggling between 80 deg and 130 deg. The MERLIN image reveals that the jet extends to 0.6 arcsec at a PA 135+-12 degr. The radio core in the VLBI images has a brightness temperature approaching the equipartition limit, indicating highly relativistic plasma beamed towards us. Delta PA in the source, the misalignment of the kpc- and pc-scale radio structure, is estimated about 32 degr, suggesting that PKS 1502+106 belongs to the aligned population. Four superluminal components are detected in the parsec scale jet, whose velocities are 24.2 h{-1}c, 14.3 h{-1}c, 6.8 h{-1}c and 18.1 h{-1}c. Our analysis supports the idea that the relativistic jet in PKS 1502+106 is characterised by extreme beaming and that its radio properties are similar to those of gamma-ray loud sources.
This letter reports rich X-ray jet structures found in the Chandra observation of PKS 1055+201. In addition to an X-ray jet coincident with the radio jet we detect a region of extended X-ray emission surrounding the jet as far from the core as the ra
dio hotspot to the North, and a similar extended X-ray region along the presumed path of the unseen counterjet to the Southern radio lobe. Both X-ray regions show a similar curvature to the west, relative to the quasar. We interpret this as the first example where we separately detect the X-ray emission from a narrow jet and extended, residual jet plasma over the entire length of a powerful FRII jet.
We perform fully relativistic hydrodynamic simulations of the deceleration and lateral expansion of a relativistic jet as it expands into an ambient medium. The hydrodynamic calculations use a 2D adaptive mesh refinement (AMR) code, which provides ad
equate resolution of the thin shell of matter behind the shock. We find that the sideways propagation is different than predicted by simple analytic models. The physical conditions at the sides of the jet are found to be significantly different than at the front of the jet, and most of the emission occurs within the initial opening angle of the jet. The light curves, as seen by observers at different viewing angles with respect to the jet axis, are then calculated assuming synchrotron emission. For an observer along the jet axis, we find a sharp achromatic `jet break in the light curve at frequencies above the typical synchrotron frequency, at $t_{jet}approx 5.8(E_{52}/n_1)^{1/3}(theta_0/0.2)^{8/3}$ days, while the temporal decay index $alpha$ ($F_{ u}propto t^{alpha}$) after the break is steeper than $-p$ ($alpha=-2.85$ for $p=2.5$). At larger viewing angles $t_{jet}$ increases and the jet break becomes smoother.
PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with an intervening galaxy. It exhibits symmetric achrom
atic variability, a rare form of variability that has been attributed to gravitational milli-lensing. It has been classified as a BL Lac object, and is one of the rare objects in this class with a visible counterjet. BL Lac objects have jet axes aligned close to the line of sight. It has also been classified as a compact symmetric object, which have jet axes not aligned close to the line of sight. Intensive efforts to understand this blazar have hitherto failed to resolve even the questions of the orientation of the relativistic jet, and the host galaxy. Answering these two questions is important as they challenge our understanding of jets in active galactic nuclei and the classification schemes we use to describe them. We show that the jet axis is aligned close to the line of sight and PKS 1413+135 is almost certainly not located in the apparent host galaxy, but is a background object in the redshift range $0.247 < z < 0.5$. The intervening spiral galaxy at $z = 0.247$ provides a natural host for the putative lens responsible for symmetric achromatic variability and is shown to be a Seyfert 2 galaxy. We also show that, as for the radio emission, a multizone model is needed to account for the high-energy emission.
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