721 research outputs found
X-ray Diagnostics of Thermal Conditions of the Hot Plasmas in the Centaurus Cluster
X-ray data of the Centaurus cluster, obtained with {\it XMM-Newton} for 45
ksec, were analyzed. Deprojected EPIC spectra from concentric thin shell
regions were reproduced equally well by a single-phase plasma emission model,
or by a two-phase model developed by {\it ASCA}, both incorporating cool
(1.7--2.0 keV) and hot ( keV) plasma temperatures. However, EPIC
spectra with higher statistics, accumulated over 3-dimentional thick shell
regions, were reproduced better by the two-phase model than by the singe-phase
one. Therefore, hot and cool plasma phases are inferred to co-exist in the
cluster core region within kpc. The iron and silicon abundances of
the plasma were reconfirmed to increase significantly towards the center, while
that of oxygen was consistent with being radially constant. The implied
non-solar abundance ratios explains away the previously reported excess X-ray
absorption from the central region. Although an additional cool (
keV) emission was detected within kpc of the center, the RGS data
gave tight upper limits on any emission with a tempeartures below
keV. These results are compiled into a magnetosphere model, which interprets
the cool phase as confined within closed magnetic loops anchored to the cD
galaxy. When combined with so-called Rosner-Tucker-Vaiana mechanism which
applies to solar coronae, this model can potentially explain basic properties
of the cool phase, including its temperature and thermal stability.Comment: 53 pages, 11 figures, accepted for publication in Astrophysical
Journa
The abundance pattern of O, Mg, Si and Fe in the intracluster medium of the Centaurus cluster observed with XMM-Newton
The abundances of O, Mg, Si and Fe in the intracluster medium of the Centaurus cluster are derived. The Fe abundance has a negative radial gradient. In solar units, the Si abundance is close to the Fe abundance, while the O and Mg abundances are much smaller. The high Fe/O and Si/O ratio indicate that metal supply from supernovae Ia is important and supernovae Ia synthesize Si as well as Fe. Within 2, the O and Mg abundances are consistent with the stellar metallicity of the cD galaxy derived from the Mg index. This result indicates that the central gas is dominated by the gas from the cD galaxy. The observed abundance pattern of the Centaurus cluster resembles to those observed in center of other clusters and groups of galaxies. However, the central Fe abundance and the Si/Fe ratio are 40 % higher and 30% smaller than those of M 87, respectively. Since the accumulation timescale of the supernovae Ia is higher in the Centaurus cluster, these differences imply a time dependence of nucleosynthesis by supernovae Ia
Implications of the central metal abundance peak in cooling core clusters of galaxies
Recent XMM-Newton observations of clusters of galaxies have provided detailed
information on the distribution of heavy elements in the central regions of
clusters with cooling cores providing strong evidence that most of these metals
come from recent SN type Ia. In this paper we compile information on the
cumulative mass profiles of iron, the most important metallicity tracer. We
find that long enrichment times (larger than 5 Gyr) are necessary to produce
the central abundance peaks. Classical cooling flows, a strongly convective
intracluster medium, and a complete metal mixing by cluster mergers would
destroy the observed abundance peaks too rapidly. Thus the observations set
strong constraints on cluster evolution models requiring that the cooling cores
in clusters are preserved over very long times. We further conclude from the
observations that the innermost part of the intracluster medium is most
probably dominated by gas originating predominantly from stellar mass loss of
the cD galaxy.Comment: 5 pages, 4 figures, A&A in press. Astronomy and Astrophysics Letters,
in pres
Detection of an X-Ray Hot Region in the Virgo Cluster of Galaxies with ASCA
Based on mapping observations with ASCA, an unusual hot region with a spatial
extent of 1 square degree was discovered between M87 and M49 at a center
coordinate of R. A. = 12h 27m 36s and Dec. = (J2000). The X-ray
emission from the region has a 2-10 keV flux of ergs
s cm and a temperature of keV, which is
significantly higher than that in the surrounding medium of keV. The
internal thermal energy in the hot region is estimated to be ergs with a gas density of cm. A power-law
spectrum with a photon index is also allowed by the data. The hot
region suggests there is an energy input due to a shock which is probably
caused by the motion of the gas associated with M49, infalling toward the M87
cluster with a velocity km s.Comment: 12 pages, 3 figures, accepted to ApJ
X-ray Measurements of the Gravitational Potential Profile in the Central Region of the Abell 1060 Cluster of Galaxies
X-ray spectral and imaging data from ASCA and ROSAT were used to measure the
total mass profile in the central region of Abell 1060, a nearby and relatively
poor cluster of galaxies. The ASCA X-ray spectra, after correcting for the
spatial response of the X-ray telescope, show an isothermal distribution of the
intra-cluster medium (ICM) within at least 12' (or kpc;
km sMpc) in radius of the cluster center. The
azimuthally averaged surface brightness profile from the ROSAT PSPC exhibits a
central excess above an isothermal model. The ring-sorted ASCA GIS
spectra and the radial surface brightness distribution from the ROSAT PSPC were
simultaneously utilized to constrain the gravitational potential profile. Some
analytic models of the total mass density profile were examined. The ICM
density profile was also specified by analytic forms. The ICM temperature
distribution was constrained to satisfy the hydrostatic equilibrium, and to be
consistent with the data. Then, the total mass distribution was found to be
described better by the universal dark halo profile proposed by Navarro, Frenk,
and White (1996;1997) than by a King-type model with a flat density core. A
profile with a central cusp together with a logarithmic radial slope of was also consistent with the data. Discussions are made concerning the
estimated dark matter distribution around the cluster center.Comment: 32 pages. Accepted: ApJ 2000, 35 pages, Title was correcte
The Structure of the X-Ray Emitting Gas in the Hydra-A Cluster of Galaxies
The temperature and abundance structure in the intracluster medium (ICM) of
the Hydra-A cluster of galaxies is studied with ASCA and ROSAT. The effect of
the large extended outskirts in the point-spread function of the X-Ray
Telescope on ASCA is included in this analysis. In the X-ray brightness
profile, the strong central excess above a single beta-model, identified in the
Einstein and ROSAT data, is also found in the harder energy band (>4keV). A
simultaneous fit of five annular spectra taken with the GIS instrument shows a
radial distribution of the temperature and metal abundance. A significant
central enhancement in the abundance distribution is found, while the
temperature profile suggests that the ICM is approximately isothermal with the
temperature of ~3.5keV. The ROSAT PSPC spectrum in the central 1'.5 region
indicates a significantly lower temperature than the GIS result. A joint
analysis of the GIS and PSPC data reveals that the spectra can be described by
a two temperature model as well as by a cooling flow model. In both cases, the
hot phase gas with the temperature of ~3.5keV occupies more than 90% of the
total emission measure within 1'.5 from the cluster center. The estimated mass
of the cooler (0.5-0.7keV) component is ~2-6 x 10^9 M_solar, which is
comparable to the mass of hot halos seen in non-cD ellipticals. The cooling
flow model gives the mass deposition rate of 60+-30 M_solar/yr, an order of
magnitude lower than the previous estimation.Comment: 27 pages, 14 figures, AAS LATEX macros v4.0, to appear in The
Astrophysical Journa
A microscopic derivation of the quantum mechanical formal scattering cross section
We prove that the empirical distribution of crossings of a "detector''
surface by scattered particles converges in appropriate limits to the
scattering cross section computed by stationary scattering theory. Our result,
which is based on Bohmian mechanics and the flux-across-surfaces theorem, is
the first derivation of the cross section starting from first microscopic
principles.Comment: 28 pages, v2: Typos corrected, layout improved, v3: Typos corrected.
Accepted for publication in Comm. Math. Phy
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