5,528 research outputs found
A giant radio halo in the massive and merging cluster Abell 1351
We report on the detection of diffuse radio emission in the X-ray luminous
and massive galaxy cluster A1351 (z=0.322) using archival Very Large Array data
at 1.4 GHz. Given its central location, morphology, and Mpc-scale extent, we
classify the diffuse source as a giant radio halo. X-ray and weak lensing
studies show A1351 to be a system undergoing a major merger. The halo is
associated with the most massive substructure. The presence of this source is
explained assuming that merger-driven turbulence may re-accelerate high-energy
particles in the intracluster medium and generate diffuse radio emission on the
cluster scale. The position of A1351 in the logP - logL plane
is consistent with that of all other radio-halo clusters known to date,
supporting a causal connection between the unrelaxed dynamical state of massive
() clusters and the presence of giant radio halos.Comment: 4 pages, 3 figures, proof corrections include
The very steep spectrum radio halo in Abell 697
In this paper we present a detailed study of the giant radio halo in the
galaxy cluster Abell 697, with the aim to constrain its origin and connection
with the cluster dynamics. We performed high sensitivity GMRT observations at
325 MHz, which showed that the radio halo is much brighter and larger at this
frequency, compared to previous 610 MHz observations. In order to derive the
integrated spectrum in the frequency range 325 MHz--1.4 GHz, we re--analysed
archival VLA data at 1.4 GHz and made use of proprietary GMRT data at 610 MHz.
{Our multifrequency analysis shows that the total radio spectrum of the giant
radio halo in A\,697 is very steep, with . %\pm0.1$. Due to energy arguments, a hadronic origin of the
halo is disfavoured by such steep spectrum. Very steep spectrum halos in
merging clusters are predicted in the case that the emitting electrons are
accelerated by turbulence, observations with the upcoming low frequency arrays
will be able to test these expectations.}Comment: 10 pages, 8 figures, A&A in pres
Dynamical locality of the nonminimally coupled scalar field and enlarged algebra of Wick polynomials
We discuss dynamical locality in two locally covariant quantum field
theories, the nonminimally coupled scalar field and the enlarged algebra of
Wick polynomials. We calculate the relative Cauchy evolution of the enlarged
algebra, before demonstrating that dynamical locality holds in the nonminimally
coupled scalar field theory. We also establish dynamical locality in the
enlarged algebra for the minimally coupled massive case and the conformally
coupled massive case.Comment: 39p
X-ray Emission Processes in Extragalactic Jets, Lobes and Hot Spots
This paper is a brief review of the processes responsible for X-ray emission
from radio jets, lobes and hot spots. Possible photons in inverse Compton
scattering models include the radio synchrotron radiation itself (i.e.
synchrotron self-Compton [SSC] emission), the cosmic microwave background
(CMB), the galaxy starlight and radiation from the active nucleus. SSC emission
has been detected from a number of hot spots. Scattering of the CMB is expected
to dominate for jets (and possibly hot spots) undergoing bulk relativistic
motion close to the direction towards the observer. Scattering of infrared
radiation from the AGN should be observable from radio lobes, especially if
they are close to the active nucleus. Synchrotron radiation is detected in some
sources, most notably the jet of M87. I briefly discuss why different hot spots
emit X-rays by different emission mechanisms and the nature of the synchrotron
spectra.Comment: To be published in the proceedings of the Bologna conference ``The
Physics of Relativistic Jets in the Chandra and XMM Era'', New Astronomy
Revie
The cluster relic source in A521
We present high sensitivity radio observations of the merging cluster A521,
at a mean redsfhit z=0.247. The observations were carried out with the GMRT at
610 MHz and cover a region of 1 square degree, with a sensitivity limit
of = 35 Jy b. The most relevant result of these
observations is the presence of a radio relic at the cluster periphery, at the
edge of a region where group infalling into the main cluster is taking place.
Thanks to the wealth of information available in the literature in the optical
and X-ray bands, a multi--band study of the relic and its surroundings was
performed. Our analysis is suggestive of a connection between this source and
the complex ongoing merger in the A521 region. The relic might be ``revived'
fossil radio plasma through adiabatic compression of the magnetic field or
shock re--acceleration due to the merger events. We also briefly discussed the
possibility that this source is the result of induced ram pressure stripping of
radio lobes associated with the nearby cluster radio galaxy J0454--1016a.
Allowing for the large uncertainties due to the small statistics, the number of
radio emitting early--type galaxies found in A521 is consistent with the
expectations from the standard radio luminosity function for local (z0.09)
cluster ellipticals.Comment: 30 pages 8 figures, 5 tables, accepted by New Astronom
GMRT Radio Halo Survey in galaxy clusters at z = 0.2 -- 0.4. II.The eBCS clusters and analysis of the complete sample
We present the results of the GMRT cluster radio halo survey. The main
purposes of our observational project are to measure which fraction of massive
galaxy clusters in the redshift range z=0.2--0.4 hosts a radio halo, and to
constrain the expectations of the particle re--acceleration model for the
origin of the non--thermal radio emission. We selected a complete sample of 50
clusters in the X-ray band from the REFLEX (27) and the eBCS (23) catalogues.
In this paper we present Giant Metrewave Radio Telescope (GMRT) observations at
610 MHz for all clusters still lacking high sensitivity radio information, i.e.
16 eBCS and 7 REFLEX clusters, thus completing the radio information for the
whole sample. The typical sensitivity in our images is in the range 1Jy b. We found a radio halo in A697, a diffuse
peripheral source of unclear nature in A781, a core--halo source in Z7160, a
candidate radio halo in A1682 and ``suspect'' central emission in Z2661.
Including the literature information, a total of 10 clusters in the sample host
a radio halo. A very important result of our work is that 25 out of the 34
clusters observed with the GMRT do not host extended central emission at the
sensitivity level of our observations, and for 20 of them firm upper limits to
the radio power of a giant radio halo were derived. The GMRT Radio Halo Survey
shows that radio halos are not common, and our findings on the fraction of
giant radio halos in massive clusters are consistent with the statistical
expectations based on the re--acceleration model. Our results favour primary to
secondary electron models.Comment: A&A in press, 17 pages, 12 figures, 4 tables Version with high
quality figures available on web at
http://www.ira.inaf.it/~tventuri/pap/Venturi_web.pd
Radio halos in merging clusters of galaxies
We present the preliminary results of 235 MHz, 327 MHz and 610 MHz
observations of the galaxy cluster A3562 in the core of the Shapley
Concentration. The purpose of these observations, carried out with the Giant
Metrewave Radio Telescope (GMRT, Pune, India) was to study the radio halo
located at the centre of A3562 and determine the shape of its radio spectrum at
low frequencies, in order to understand the origin of this source. In the
framework of the re--acceleration model, the preliminary analysis of the halo
spectrum suggests that we are observing a young source (few yrs) at the
beginning of the re--acceleration phase.Comment: 3 pages, 2 figures. Proceedings of IAU Colloquium 195 - Outskirts of
Galaxy Clusters: intense life in the suburb
Supersymmetric Field-Theoretic Models on a Supermanifold
We propose the extension of some structural aspects that have successfully
been applied in the development of the theory of quantum fields propagating on
a general spacetime manifold so as to include superfield models on a
supermanifold. We only deal with the limited class of supermanifolds which
admit the existence of a smooth body manifold structure. Our considerations are
based on the Catenacci-Reina-Teofillatto-Bryant approach to supermanifolds. In
particular, we show that the class of supermanifolds constructed by
Bonora-Pasti-Tonin satisfies the criterions which guarantee that a
supermanifold admits a Hausdorff body manifold. This construction is the
closest to the physicist's intuitive view of superspace as a manifold with some
anticommuting coordinates, where the odd sector is topologically trivial. The
paper also contains a new construction of superdistributions and useful results
on the wavefront set of such objects. Moreover, a generalization of the
spectral condition is formulated using the notion of the wavefront set of
superdistributions, which is equivalent to the requirement that all of the
component fields satisfy, on the body manifold, a microlocal spectral condition
proposed by Brunetti-Fredenhagen-K\"ohler.Comment: Final version to appear in J.Math.Phy
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