305 research outputs found
Electrolytic separation of crystals of transition-metal oxides
Versatile flux system grows large, well-formed, stoichiometric single crystals of mixed oxides of the transition-metal elements. These crystals have important uses in the microwave field, and applications as lasers and masers in communications
Chandra Observation of the Cluster Environment of a WAT Radio Source in Abell 1446
Wide-angle tail (WAT) radio sources are often found in the centers of galaxy
clusters where intracluster medium (ICM) ram pressure may bend the lobes into
their characteristic C-shape. We examine the low redshift (z=0.1035) cluster
Abell 1446, host to the WAT radio source 1159+583. The cluster exhibits
possible evidence for a small-scale cluster-subcluster merger as a cause of the
WAT radio source morphology. This evidence includes the presence of temperature
and pressure substructure along the line that bisects the WAT as well as a
possible wake of stripped interstellar material or a disrupted cool core to the
southeast of the host galaxy. A filament to the north may represent cool,
infalling gas that's contributing to the WAT bending while spectroscopically
determined redshifts of member galaxies may indicate some component of a merger
occurring along the line-of-sight. The WAT model of high flow velocity and low
lobe density is examined as another scenario for the bending of 1159+583. It
has been argued that such a model would allow the ram pressure due to the
galaxy's slow motion through the ICM to shape the WAT source. A temperature
profile shows that the cluster is isothermal (kT= 4.0 keV) in a series of
annuli reaching a radius of 400 kpc. There is no evidence of an ongoing cooling
flow. Temperature, abundance, pressure, density, and mass profiles, as well as
two-dimensional maps of temperature and pressure are presented.Comment: 40 AASTeX pages including 15 postscript figures; accepted for
publication in Ap
Deep radio observations of the radio halo of the bullet cluster 1E 0657-55.8
We present deep 1.1-3.1 GHz Australia Telescope Compact Array observations of
the radio halo of the bullet cluster, 1E 0657-55.8. In comparison to existing
images of this radio halo the detection in our images is at higher
significance. The radio halo is as extended as the X-ray emission in the
direction of cluster merger but is significantly less extended than the X-ray
emission in the perpendicular direction. At low significance we detect a faint
second peak in the radio halo close to the X-ray centroid of the smaller
sub-cluster (the bullet) suggesting that, similarly to the X-ray emission, the
radio halo may consist of two components. Finally, we find that the distinctive
shape of the western edge of the radio halo traces out the X-ray detected bow
shock. The radio halo morphology and the lack of strong point-to-point
correlations between radio, X-ray and weak-lensing properties suggests that the
radio halo is still being formed. The colocation of the X-ray shock with a
distinctive radio brightness edge illustrates that the shock is influencing the
structure of the radio halo. These observations support the theory that shocks
and turbulence influence the formation and evolution of radio halo synchrotron
emission.Comment: 15 pages, 16 figures, 3 tables. Accepted by MNRA
VLBI Observations of a Complete Sample of Radio Galaxies V. 3C346 and 4C31.04: two Unusual CSS Sources
We present observations at 1.7 and 8.4 GHz of two Compact Steep Spectrum
(CSS) sources from a complete sample of low-intermediate power radio galaxies.
3C346 shows an asymmetric structure with a one-sided ``jet'' and ``hot spot''.
Present observations suggest that the classification of this source as a CSS is
inappropriate, and that it is a common radio galaxy at a small angle to the
line of sight. Its properties are in agreement with the predictions of unified
schemes models. 4C31.04 shows more complex structure with the possibility of a
centrally located flat spectrum core in between two close lobes. We suggest
that this source could be a low redshift Compact Symmetric Object.Comment: 15 pages, LATEX, uuenconde ps figures To be published in the
Astrophysical Journal, October 20th issu
The Broad Line Radio Galaxy J2114+820
In the frame of the study of a new sample of large angular size radio
galaxies selected from the NRAO VLA Sky Survey, we have made radio observations
of J2114+820, a low power radio galaxy with an angular size of 6'. Its radio
structure basically consists of a prominent core, a jet directed in north-west
direction and two extended S-shaped lobes. We have also observed the optical
counterpart of J2114+820, a bright elliptical galaxy with a strong unresolved
central component. The optical spectrum shows broad emission lines. This fact,
together with its low radio power and FR-I type morphology, renders J2114+820 a
non-trivial object from the point of view of the current unification schemes of
radio loud active galactic nuclei.Comment: 6 pages, 5 figures. To appear in the proceedings of EVN/JIVE
Symposium No. 4, New Astronomy Reviews (eds. Garrett et al.
Parsec Scale Properties of Markarian 501
We present the results of a high angular resolution study of the BL Lac
object Markarian 501 in the radio band. We consider data taken at 14 different
epochs, ranging between 1.6 GHz and 22 GHz in frequency, and including new
Space VLBI observations obtained on 2001 March 5 and 6 at 1.6 and 5 GHz. We
study the kinematics of the parsec-scale jet and estimate its bulk velocity and
orientation with respect to the line of sight. Limb brightened structure in the
jet is clearly visible in our data and we discuss its possible origin in terms
of velocity gradients in the jet. Quasi-simultaneous multi-wavelength
observations allow us to map the spectral index distribution and to compare it
to the jet morphology. Finally, we estimate the physical parameters of the
parsec-scale jet.Comment: accepted for publication in ApJ; 24 pages with 17 figures (fig. 1 and
fig. 2 available only as .jpg files
Prospects of detecting gamma-ray emission from galaxy clusters: cosmic rays and dark matter annihilations
We study the possibility for detecting gamma-ray emission from galaxy
clusters. We consider 1) leptophilic models of dark matter (DM) annihilation
that include a Sommerfeld enhancement (SFE), 2) different representative
benchmark models of supersymmetric DM, and 3) cosmic ray (CR) induced pion
decay. Among all clusters/groups of a flux-limited X-ray sample, we predict
Virgo, Fornax and M49 to be the brightest DM sources and find a particularly
low CR-induced background for Fornax. For a minimum substructure mass given by
the DM free-streaming scale, cluster halos maximize the substructure boost for
which we find a factor above 1000. Since regions around the virial radius
dominate the annihilation flux of substructures, the resulting surface
brightness profiles are almost flat. This makes it very challenging to detect
this flux with imaging atmospheric Cherenkov telescopes. Assuming cold dark
matter with a substructure mass distribution down to an Earth mass and using
extended Fermi upper limits, we rule out the leptophilic models in their
present form in 28 clusters, and limit the boost from SFE in M49 and Fornax to
be < 5. This corresponds to a limit on SFE in the Milky Way of < 3, which is
too small to account for the increasing positron fraction with energy as seen
by PAMELA and challenges the DM interpretation. Alternatively, if SFE is
realized in Nature, this would imply a limiting substructure mass of M_lim >
10^4 M_sol - a problem for structure formation. Using individual cluster
observations, it will be challenging for Fermi to constrain our selection of DM
benchmark models without SFE. The Fermi upper limits are, however, closing in
on our predictions for the CR flux using an analytic model based on
cosmological hydrodynamical cluster simulations. We limit the CR-to-thermal
pressure in nearby bright galaxy clusters of the Fermi sample to < 10% and in
Norma and Coma to < 3%.Comment: 43 pages, 23 figures, 10 tables. Accepted for publication in Phys.
Rev. D: streamlined paper, added a paragraph about detectability to
introduction, few references added, and few typos correcte
The highest frequency detection of a radio relic : 16 GHz AMI observations of the 'Sausage' cluster
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society: Letters. © 2014 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We observed the cluster CIZA J2242.8+5301 with the Arcminute Microkelvin Imager at 16 GHz and present the first high radio-frequency detection of diffuse, non-thermal cluster emission. This cluster hosts a variety of bright, extended, steep-spectrum synchrotron-emitting radio sources, associated with the intracluster medium, called radio relics. Most notably, the northern, Mpc-wide, narrow relic provides strong evidence for diffusive shock acceleration in clusters. We detect a puzzling, flat-spectrum, diffuse extension of the southern relic, which is not visible in the lower radio-frequency maps. The northern radio relic is unequivocally detected and measures an integrated flux of 1.2 ± 0.3 mJy. While the low-frequency (<2 GHz) spectrum of the northern relic is well represented by a power law, it clearly steepens towards 16 GHz. This result is inconsistent with diffusive shock acceleration predictions of ageing plasma behind a uniform shock front. The steepening could be caused by an inhomogeneous medium with temperature/density gradients or by lower acceleration efficiencies of high energy electrons. Further modelling is necessary to explain the observed spectrum.Peer reviewe
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