7,726 research outputs found
1.4-GHz observations of extended giant radio galaxies
This paper presents 1.4-GHz radio continuum observations of 15 very extended
radio galaxies. These sources are so large that most interferometers lose
partly their structure and total flux density. Therefore, single-dish
detections are required to fill in the central (u,v) gap of interferometric
data and obtain reliable spectral index patterns across the structures, and
thus also an integrated radio continuum spectrum. We have obtained such 1.4-GHz
maps with the 100-m Effelsberg telescope and combined them with the
corresponding maps available from the NVSS. The aggregated data allow us to
produce high-quality images, which can be used to obtain physical parameters of
the mapped sources. The combined images reveal in many cases extended low
surface-brightness cocoons.Comment: 39 pages, 19 figures, 3 tables. Published in Ac
Large-Scale Radio Structure in the Universe: Giant Radio Galaxies
Giant radio galaxies (GRGs), with linear sizes larger than 1 Mpc (H0=50
km/s/Mpc), represent the biggest single objects in the Universe. GRGs are rare
among the entire population of radio galaxies (RGs) and their physical
evolution is not well understood though for many years they have been of
special interest for several reasons. The lobes of radio sources can compress
cold gas clumps and trigger star or even dwarf galaxy formation, they can also
transport gas from a host galaxy to large distances and seed the IGM with
magnetic fields. Since GRGs have about 10 to 100 times larger sizes than normal
RGs, their influence on the ambient medium is correspondingly wider and is
pronounced on scales comparable to those of clusters of galaxies or larger.
Therefore `giants' could play an important role in the process of large-scale
structure formation in the Universe. Recently, thanks to the new all sky radio
surveys, significant progress in searching for new GRGs has been made.Comment: To appear in Multiwavelength AGN Surveys, ed. R. Maiolino and R.
Mujica, Singapore: World Scientific, 2004, 2 page
Multi-Frequency Study of the B3-VLA Sample II. The Database
We present total flux densities of 1049 radio sources in the frequency range
from 151 MHz to 10.6 GHz. These sources belong to the B3-VLA sample, which is
complete down to 100 mJy at 408 MHz. The data constitute a homogeneous spectral
database for a large sample of radio sources, 50 times fainter than the 3C
catalogue, and will be used to perform a spectral ageing analysis, which is one
of the critical points in understanding the physics and evolution of
extragalactic radio sources.Comment: 14 pages, 3 figures, accepted for publication in Astronomy &
Astrophysics Supplement Series, gzipped postscript file also available at
http://multivac.jb.man.ac.uk:8000/ceres/papers/papers.html or
http://gladia.astro.rug.nl:8000/ceres/papers/papers.htm
Signatures of restarted activity in core-dominated, triple radio sources selected from the FIRST survey
Signatures of the re-occurrence of activity in radio-loud AGNs, indicated
either by the so-called double-double or X-shaped structures, have been
observed in a number of radio sources. All such objects known to date have
linear sizes of the order of a megaparsec. A number of the sources that are
appreciably more compact than this, but that exhibit hints of a past phase of
activity, were found in the VLA FIRST survey. Their structures show symmetric
relic lobes straddling relatively bright, unresolved cores. Observations of the
cores of 15 such structures with MERLIN at 5 GHz have shown that four of them
are doubles or core-jets on the subarcsecond scale. Misalignments of \Delta PA
\ga 30 degr. between the axis of the inner structure and the line connecting
the fitted maxima of the arcminute-scale relic lobes are clearly visible in
three of the four sources. From these results, we can infer that a rapid
repositioning of the central engine in each of these three radio sources is the
most plausible interpretation of the observed morphology and that a merger is
most likely the original cause of such a repositioning. In the case of TXS
1033+026, the optical image extracted from the SDSS archives clearly suggests
that two objects separated by only 2.7 kpc (projected onto the sky plane) are
indeed merging. The inner parts of TXS 0818+214 and TXS 1312+563 could be
interpreted as double-lobed, and consequently, these sources could be of the
double-double type; but further multifrequency observations are necessary to
provide support for such an interpretation.Comment: 9 pages, 5 figures, matches the version printed in Astronomy &
Astrophysics, very minor correction of Table
In-Situ Particle Acceleration in Extragalactic Radio Hot Spots: Observations Meet Expectations
We discuss, in terms of particle acceleration, the results from optical VLT
observations of hot spots associated with radio galaxies. On the basis of
observational and theoretical grounds, it is shown that:
1. relatively low radio-radio power hot spots are the optimum candidates for
being detected at optical waves. This is supported by an unprecedented optical
detection rate of 70% out of a sample of low radio power hot spots.
2. the shape of the synchrotron spectrum of hot spots is mainly determined by
the strength of the magnetic field in the region. In particular, the break
frequency, related to the age of the oldest electrons in the hot spots, is
found to increase with decreasing synchrotron power and magnetic field
strength.
Both observational results are in agreement with an in-situ particle
acceleration scenario.Comment: 5 pages, TeX (or Latex, etc), 4 figures, to appear in MNRAS Letter,
Updated reference
Deriving AGN properties from radio CP and LP
We report multi-frequency circular polarization measurements for the radio
source 0056-00 taken at the Effelsberg 100-m radiotelescope. The data reduction
is based on a new calibration procedure that allows the contemporary
measurement of the four Stokes parameters with single-dish radiotelescopesComment: 2 pages, Proceeding of "IAU Symposium No.259. Cosmic Magnetic Fields
from planets, to stars and galaxies
Factorizing Numbers with the Gauss Sum Technique: NMR Implementations
Several physics-based algorithms for factorizing large number were recently
published. A notable recent one by Schleich et al. uses Gauss sums for
distinguishing between factors and non-factors. We demonstrate two NMR
techniques that evaluate Gauss sums and thus implement their algorithm. The
first one is based on differential excitation of a single spin magnetization by
a cascade of RF pulses. The second method is based on spatial averaging and
selective refocusing of magnetization for Gauss sums corresponding to factors.
All factors of 16637 and 52882363 are successfully obtained.Comment: 4 pages, 4 figures; Abstract and Conclusion are slightly modified.
References added and formatted with Bibte
The spectral-curvature parameter: an alternative tool for the analysis of synchrotron spectra
The so-called Spectral Curvature Parameter(SCP), when plotted versus the
high-frequency spectral index () of synchrotron sources, provides
crucial parameters on the continuum spectrum of synchrotron radiation without
the more complex modeling of spectral ageing scenarios. An important merit of
the SCP- diagram is the enhanced reliability of extracting multiple
injection spectra, . Different from the colour-colour diagram,
tracks of different s, especially when the synchrotron particles
are young, exhibit less overlap and less smearing in the SCP- diagram.
Three giant radio galaxies(GRGs) and a sample of Compact steep spectrum(CSS)
souces are presented. GRGs exhibit asymmetries of their injection spectral
indices in the SCP- diagram. The obtained
s and the trends in the sources are cross-checked with the
literature and show remarkable confidence. Besides the spectral steepening,
spectral flattening is prominent in the radio lobes. The spectral flattening is
a clue to efficient re-acceleration processes in the lobes. It implies
interaction with the surrounding intergalactic or intra-cluster medium is an
important characteristic of GRGs. In the SW lobe of DA240, there is a clear
sign of CI and KP/JP bifurcation at the source extremity. This indicates a
highly relativistic energy transportation from the core or in situ acceleration
in this typical FR I lobe. Our analysis proves, if exists, KP spectra imply the
existence of strong field with . In the CSS
sources, our result confirms the CI model and . The
synchrotron self-absorption is significant in the CSS sample.Comment: to be published in A&
Center vortex properties in the Laplace center gauge of SU(2) Yang-Mills theory
Resorting to the the Laplace center gauge (LCG) and to the Maximal-center
gauge (MCG), respectively, confining vortices are defined by center projection
in either case. Vortex properties are investigated in the continuum limit of
SU(2) lattice gauge theory. The vortex (area) density and the density of vortex
crossing points are investigated. In the case of MCG, both densities are
physical quantities in the continuum limit. By contrast, in the LCG the
piercing as well as the crossing points lie dense in the continuum limit. In
both cases, an approximate treatment by means of a weakly interacting vortex
gas is not appropriate.Comment: reference added, submitted to Phys. Lett.
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