4,814 research outputs found
Suzaku Detection of Thermal X-Ray Emission Associated with the Western Radio Lobe of Fornax A
We present the results of X-ray mapping observations of the western radio
lobe of the Fornax A galaxy, using the X-ray Imaging Spectrometer (XIS) onboard
the Suzaku satellite with a total exposure time of 327 ks. The purpose of this
study is to investigate the nature and spatial extent of the diffuse thermal
emission around the lobe by exploiting the low and stable background of the
XIS. The diffuse thermal emission had been consistently reported in all
previous studies of this region, but its physical nature and relation to the
radio lobe had not been examined in detail. Using the data set covering the
entire western lobe and the central galaxy NGC 1316, as well as comparison sets
in the vicinity, we find convincingly the presence of thermal plasma emission
with a temperature of ~1 keV in excess of conceivable background and
contaminating emission (cosmic X-ray background, Galactic halo, intra-cluster
gas of Fornax, interstellar gas of NGC 1316, and the ensemble of point-like
sources). Its surface brightness is consistent with having a spherical
distribution peaking at the center of the western lobe with a projected radius
of ~12 arcmin. If the volume filling factor of the thermal gas is assumed to be
unity, its estimated total mass amounts to ~10^{10} M_sun, which would be
~10^{2} times that of the central black hole and comparable to that of the
current gas mass of the host galaxy. Its energy density is comparable to or
larger than those in the magnetic field and non-thermal electrons responsible
for the observed radio and X-ray emission.Comment: 10 pages, 5 figures, accepted for publication in PAS
Evidence of non-thermal X-ray emission from radio lobes of Cygnus A
Using deep Chandra ACIS observation data for Cygnus A, we report evidence of
non-thermal X-ray emission from radio lobes surrounded by a rich intra-cluster
medium (ICM). The diffuse X-ray emission, which are associated with the eastern
and western radio lobes, were observed in a 0.7--7 keV Chandra$ ACIS image. The
lobe spectra are reproduced with not only a single-temperature Mekal model,
such as that of the surrounding ICM component, but also an additional power-law
(PL) model. The X-ray flux densities of PL components for the eastern and
western lobes at 1 keV are derived as 77.7^{+28.9}_{-31.9} nJy and
52.4^{+42.9}_{-42.4} nJy, respectively, and the photon indices are
1.69^{+0.07}_{-0.13} and 1.84^{+2.90}_{-0.12}, respectively. The non-thermal
component is considered to be produced via the inverse Compton (IC) process, as
is often seen in the X-ray emission from radio lobes. From a re-analysis of
radio observation data, the multiwavelength spectra strongly suggest that the
seed photon source of the IC X-rays includes both cosmic microwave background
radiation and synchrotron radiation from the lobes. The derived parameters
indicate significant dominance of the electron energy density over the magnetic
field energy density in the Cygnus A lobes under the rich ICM environment.Comment: 8 pages, 5 figures, accepted for publication in Ap
Two remarks on -projectivity of Riemannian metrics
We show that -projectivity of two Riemannian metrics
introduced in \cite{Top2003} implies affine equivalence of the metrics unless
. Moreover, we show that for ,
-projectivity implies projective equivalence.Comment: 6 pages, 2 figure
Kaehler Manifolds of Quasi-Constant Holomorphic Sectional Curvatures
The Kaehler manifolds of quasi-constant holomorphic sectional curvatures are
introduced as Kaehler manifolds with complex distribution of codimension two,
whose holomorphic sectional curvature only depends on the corresponding point
and the geometric angle, associated with the section. A curvature identity
characterizing such manifolds is found. The biconformal group of
transformations whose elements transform Kaehler metrics into Kaehler ones is
introduced and biconformal tensor invariants are obtained. This makes it
possible to classify the manifolds under consideration locally. The class of
locally biconformal flat Kaehler metrics is shown to be exactly the class of
Kaehler metrics whose potential function is only a function of the distance
from the origin in complex Euclidean space. Finally we show that any rotational
even dimensional hypersurface carries locally a natural Kaehler structure,
which is of quasi-constant holomorphic sectional curvatures.Comment: 36 page
Study of systematics effects on the Cross Power Spectrum of 21 cm Line and Cosmic Microwave Background using Murchison Widefield Array Data
Observation of the 21cm line signal from neutral hydrogen during the Epoch of
Reionization is challenging due to extremely bright Galactic and extragalactic
foregrounds and complicated instrumental calibration. A reasonable approach for
mitigating these problems is the cross correlation with other observables. In
this work, we present the first results of the cross power spectrum (CPS)
between radio images observed by the Murchison Widefield Array and the cosmic
microwave background (CMB), measured by the Planck experiment. We study the
systematics due to the ionospheric activity, the dependence of CPS on group of
pointings, and frequency. The resulting CPS is consistent with zero because the
error is dominated by the foregrounds in the 21cm observation. Additionally,
the variance of the signal indicates the presence of unexpected systematics
error at small scales. Furthermore, we reduce the error by one order of
magnitude with application of a foreground removal using a polynomial fitting
method. Based on the results, we find that the detection of the 21cm-CMB CPS
with the MWA Phase I requires more than 99.95% of the foreground signal
removed, 2000 hours of deep observation and 50% of the sky fraction coverage.Comment: 15 pages, 16 figures, accepted to MNRA
Interaction of massless Dirac field with a Poincar\'e gauge field
In this paper we consider a model of Poincar\'e gauge theory (PGT) in which a
translational gauge field and a Lorentz gauge field are actually identified
with the Einstein's gravitational field and a pair of ``Yang-Mills'' field and
its partner, respectively.In this model we re-derive some special solutions and
take up one of them. The solution represents a ``Yang-Mills'' field without its
partner field and the Reissner-Nordstr\"om type spacetime, which are generated
by a PGT-gauge charge and its mass.It is main purpose of this paper to
investigate the interaction of massless Dirac fields with those fields. As a
result, we find an interesting fact that the left-handed massless Dirac fields
behave in the different manner from the right-handed ones. This can be
explained as to be caused by the direct interaction of Dirac fields with the
``Yang-Mills'' field. Accordingly, the phenomenon can not happen in the
behavior of the neutrino waves in ordinary Reissner-Nordstr\"om geometry. The
difference between left- and right-handed effects is calculated quantitatively,
considering the scattering problems of the massless Dirac fields by our
Reissner-Nordstr\"om type black-hole.Comment: 10pages, RevTeX3.
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