5,761 research outputs found
NGC1052 - A study of the pc-scale twin jet
We present results of a VLBA multi-frequency study of the pc-scale twin jet
in NGC1052. We observed this object at epoch 1998.99 with the VLBA at 5, 8.4,
22 and 43 GHz both in total and linearly polarized intensity. The spectral
analysis confirms the necessity of a free-free absorbing medium, obscuring the
innermost part of both jets. At 5 GHz we found a compact linearly polarized
emission region at the base of the eastern jet with a degree of polarization of
1.5%. At higher frequencies there is no evidence for polarization in our data.
A core shift analysis constrains the position of the central engine to ~0.03
pc. The shift rates of the apparent core position with frequency confirm the
strong influence of free-free absorption in conjunction with steep pressure
gradients at the bases of both jets.Comment: Proceedings of the conference "SRT: the impact of large antennas on
Radio Astronomy and Space Science", Cagliari, Italy, 7-10 November 2001, in
press; 6 pages, 5 figures, needs srt_style.st
Catching the Radio Flare in CTA 102 III. Core-Shift and Spectral Analysis
The temporal and spatial spectral evolution of the jets of AGN can be studied
with multi-frequency, multi-epoch VLBI observations. The combination of both,
morphological and spectral parameters can be used to derive source intrinsic
physical properties such as the magnetic field and the non-thermal particle
density. In the first two papers of this series, we analyzed the single-dish
light curves and the VLBI kinematics of the blazar CTA 102 and suggested a
shock-shock interaction between a traveling and a standing shock wave as a
possible scenario to explain the observed evolution of the component associated
to the 2006 flare. In this paper we investigate the core-shift and spectral
evolution to test our hypothesis of a shock-shock interaction. We used 8
multi-frequency VLBA observations to analyze the temporal and spatial evolution
of the spectral parameters during the flare. We observed CTA 102 between May
2005 and April 2007 using the VLBA at six different frequencies spanning from 2
- 86 GHz. After the calibrated VLBA images were corrected for opacity, we
performed a detailed spectral analysis. From the derived values we estimated
the magnetic field and the density of the relativistic particles. The detailed
analysis of the opacity shift reveals that the position of the jet core is
proportional to nu^-1 with some temporal variations. The value suggests
possible equipartition between magnetic field energy and particle kinetic
energy densities at the most compact regions. From the variation of the
physical parameters we deduced that the 2006 flare in CTA 102 is connected to
the ejection of a new traveling feature (t=2005.9) and the interaction between
this shock wave and a stationary structure around 0.1 mas from the core. The
source kinematics together with the spectral and structural variations can be
described by helical motions in an over-pressured jet.Comment: 35 pages, 46 figure
A precise characterisation of the top quark electro-weak vertices at the ILC
Top quark production in the process at a future linear
electron positron collider with polarised beams is a powerful tool to determine
indirectly the scale of new physics. The presented study, based on a detailed
simulation of the ILD detector concept, assumes a centre-of-mass energy of
GeV and a luminosity of
equally shared between the incoming beam polarisations of . Events are selected in which the top pair
decays semi-leptonically and the cross sections and the forward-backward
asymmetries are determined. Based on these results, the vector, axial vector
and tensorial conserving couplings are extracted separately for the photon
and the component. With the expected precision, a large number of models
in which the top quark acts as a messenger to new physics can be distinguished
with many standard deviations. This will dramatically improve expectations from
e.g. the LHC for electro-weak couplings of the top quark.Comment: This work is an update of arXiv:1307.8102, minor changes w.r.t. v1
(typos, wrong grammar, incomplete sentences etc.
Parallax and Kinematics of PSR B0919+06 from VLBA Astrometry and Interstellar Scintillometry
Results are presented from a long-term astrometry program on PSR B0919+06
using the NRAO Very Long Baseline Array. With ten observations (seven epochs)
between 1994--2000, we measure a proper motion of 18.35 +/- 0.06 mas/yr in RA,
86.56 +/- 0.12 mas/yr in Dec, and a parallax of 0.83 +/- 0.13 mas (68%
confidence intervals). This yields a pulsar distance of 1.21 +/- 0.19 kpc,
making PSR B0919+06 the farthest pulsar for which a trigonometric parallax has
been obtained, and the implied pulsar transverse speed is 505 +/- 80 km/s.
Combining the distance estimate with interstellar scintillation data spanning
20 years, we infer the existence of a patchy or clumpy scattering screen along
the line of sight in addition to the distributed electron density predicted by
models for the Galaxy, and constrain the location of this scattering region to
within about 250 parsecs of the Sun. Comparison with the lines of sight towards
other pulsars in the same quadrant of the Galaxy permits refinement of our
knowledge of the local interstellar matter in this direction.Comment: 12 pages, includes 4 figures and 3 tables, uses AASTeX 5 (included);
ApJ submitte
The Twin--Jet System in NGC 1052: VLBI-Scrutiny of the Obscuring Torus
NGC 1052 offers the possibility to study the obscuring torus around a
supermassive black hole, predicted by the standard model of active galactic
nuclei, over a wide range of wavelengths from the radio to the X-ray regime. We
present a detailed VLBI study of the parsec-scale structure of the ``twin-jet''
system in NGC 1052 in both total and polarized intensity and at multiple
frequencies. We report the detection of linearly polarized emission from the
base of the eastern jet at 5 GHz. While the radio spectrum in this region might
be still consistent with synchrotron self absorption, the highly inverted
spectrum of the western jet base represents a clear sign of pronounced
free-free absorption in a circumnuclear torus. We observe an abrupt change of
the brightness temperature gradient at a distance of pc to 0.3 pc
from the central engine. This might provide an observational signature of the
edge of the central torus, where the transition from an external
pressure-dominated jet regime to a more or less freely expanding jet takes
place. We determine the absorbing column density towards the western jet core
to be cm in good agreement with the values
derived from various X-ray observations. This suggests that the nuclear X-ray
emission and the jet emission imaged by VLBI originate on the same scales.Comment: 14 pages, 11 figures, needs aa.cls, accepted for publication in
Astronomy & Astrophysics, note that the resolution of figure 2 has been
decreased in comparison to the journal versio
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