32,673 research outputs found
The Chandra-COSMOS survey IV: X-ray spectra of the bright sample
We present the X-ray spectral analysis of the 390 brightest extragalactic
sources in the Chandra-COSMOS catalog, showing at least 70 net counts in the
0.5-7 keV band. This sample has a 100% completeness in optical-IR
identification, with 75% of the sample having a spectroscopic redshift and 25%
a photometric redshift. Our analysis allows us to accurately determine the
intrinsic absorption, the broad band continuum shape ({\Gamma}) and intrinsic
L(2-10) distributions, with an accuracy better than 30% on the spectral
parameters for 95% of the sample. The sample is equally divided in type-1
(49.7%) and type-2 AGN (48.7%) plus few passive galaxies at low z. We found a
significant difference in the distribution of {\Gamma} of type-1 and type-2,
with small intrinsic dispersion, a weak correlation of {\Gamma} with L(2-10)
and a large population (15% of the sample) of high luminosity, highly obscured
(QSO2) sources. The distribution of the X ray/Optical flux ratio (Log(FX /Fi))
for type-1 is narrow (0 < X/O < 1), while type-2 are spread up to X/O = 2. The
X/O correlates well with the amount of X-ray obscuration. Finally, a small
sample of Compton thick candidates and peculiar sources is presented. In the
appendix we discuss the comparison between Chandra and XMM-Newton spectra for
280 sources in common. We found a small systematic difference, with XMM-Newton
spectra that tend to have softer power-laws and lower obscuration.Comment: 20 pages, 16 figures. Accepted for Pubblication in MNRAS, 2013
February
Skeletally Dugundji spaces
We introduce and investigate the class of skeletally Dugundji spaces as a
skeletal analogue of Dugundji space. The main result states that the following
conditions are equivalent for a given space : (i) is skeletally
Dugundji; (ii) Every compactification of is co-absolute to a Dugundji
space; (iii) Every -embedding of the absolute in another space is
strongly -regular; (iv) has a multiplicative lattice in the sense of
Shchepin \cite{s76} consisting of skeletal maps
On noncontractible compacta with trivial homology and homotopy groups
We construct an example of a Peano continuum such that: (i) is a
one-point compactification of a polyhedron; (ii) is weakly homotopy
equivalent to a point (i.e. is trivial for all ); (iii)
is noncontractible; and (iv) is homologically and cohomologically
locally connected (i.e. is a and space). We also prove that all
classical homology groups (singular, \v{C}ech, and Borel-Moore), all classical
cohomology groups (singular and \v{C}ech), and all finite-dimensional Hawaiian
groups of are trivial
Microwave component time delays for the 70-meter antennas
The X-band feed assemblies in the 64 meter antennas were redesigned to accommodate the upgrading to 70 meters and the associated surface reshaping. To maintain time delay data logs, new calculations were made of the microwave component delays for the XRO Mod IV X-band (8.4 to 8.45 GHz) feed assembly that was installed at DSS-63, and will soon be implemented at DSS-43 and DSS-14
Supernova Remnants in the Magellanic Clouds. IV. X-Ray Emission from the Largest SNR in the LMC
We present the first X-ray detection of SNR 0450-70.9 the largest known
supernova remnant (SNR) in the Large Magellanic Cloud. To study the physical
conditions of this SNR, we have obtained XMM-Newton X-ray observations, optical
images and high-dispersion spectra, and radio continuum maps. Optical images of
SNR 0450-70.9 show a large, irregular elliptical shell with bright filaments
along the eastern and western rims and within the shell interior. The interior
filaments have higher [S II]/Halpha ratios and form an apparent inner shell
morphology. The X-ray emission region is smaller than the full extent of the
optical shell, with the brightest X-ray emission found within the small
interior shell and on the western rim of the large shell. The expansion
velocity of the small shell is ~220 km/s, while the large shell is ~120 km/s.
The radio image shows central brightening and a fairly flat radio spectral
index over the SNR. However, no point X-ray or radio source corresponding to a
pulsar is detected and the X-ray emission is predominantly thermal. Therefore,
these phenomena can be most reasonably explained in terms of the advanced age
of the large SNR. Using hydrodynamic models combined with a nonequilibrium
ionization model for thermal X-ray emission, we derived a lower limit on the
SNR age of about 45,000 yr, well into the later stages of SNR evolution.
Despite this, the temperature and density derived from spectral fits to the
X-ray emission indicate that the remnant is still overpressured, and thus that
the development is largely driven by hot gas in the SNR interior.Comment: Accepted for publication in The Astrophysical Journa
The XMM-Newton wide-field survey in the COSMOS field. IV: X-ray spectral properties of Active Galactic Nuclei
We present a detailed spectral analysis of point-like X-ray sources in the
XMM-COSMOS field. Our sample of 135 sources only includes those that have more
than 100 net counts in the 0.3-10 keV energy band and have been identified
through optical spectroscopy. The majority of the sources are well described by
a simple power-law model with either no absorption (76%) or a significant
intrinsic, absorbing column (20%).As expected, the distribution of intrinsic
absorbing column densities is markedly different between AGN with or without
broad optical emission lines. We find within our sample four Type-2 QSOs
candidates (L_X > 10^44 erg/s, N_H > 10^22 cm^-2), with a spectral energy
distribution well reproduced by a composite Seyfert-2 spectrum, that
demonstrates the strength of the wide field XMM/COSMOS survey to detect these
rare and underrepresented sources.Comment: 16 pages, ApJS COSMOS Special Issue, 2007 in press. The
full-resolution version is available at
http://www.mpe.mpg.de/XMMCosmos/PAPERS/mainieri_cosmos.ps.g
Coordinated IUE, Einstein and optical observations of accreting degenerate dwarfs
Three binary systems believed to be composed of a white dwarf and a late type star, AM Her, SS Cyg, and U Gem were observed simultaneously in the IV X-ray and optical wavelengths. The system AM Her was in its customary high state at the time of the observations, while SS Cyg and U Gem were in a low state. In all three cases, a significant UV black body component with KT approximately greater than 10 eV was found. The flux in this component is in excess of the amount predicted by current scenarios of gravitational energy release
Death, Burial and Cemeteries in Early Medieval Chersonese-Cherson: A New Book about Funeral Traditions and Ceremony in a Provincial Byzantine Town
Review on Фомин М. В. Погребальная традиция и обряд в византийском Херсоне (IV–X вв.). – Х. : Коллегиум, 2011. – 290 с
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A two - grid, fourth order method for nonlinear fourth order boundary value problems
A fourth order convergent finite difference method is developed for the numerical solution of the nonlinear fourth order boundary value
problem y(iv)(x) = f(x,y), a<x <b, y(a) = A0 , y"(a) = B0 , y(b) = A1,
y" (b) = B1 .
The method is based on a second order convergent method which is used on two grids, fourth order convergence being obtained by considering a linear combination of the individual results relating to the two grids.
Special formulas are developed for application to grid points adjacent to the boundaries x = a and x = b , the principal parts of the local truncation errors of these formulas being the same as that of the second order method used at other points of each grid.
Modifications to these special formulas are noted for problems with boundary conditions of the form y (a) = Ao , y'(a) = Co , y(b) = A1,
y'(b) =c1
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