1,355 research outputs found
Plasma turbulence simulations with X-points using the flux-coordinate independent approach
In this work, the Flux-Coordinate Independent (FCI) approach to plasma
turbulence simulations is formulated for the case of generic, static magnetic
fields, including those possessing stochastic field lines. It is then
demonstrated that FCI is applicable to nonlinear turbulent problems with and
without X-point geometry. In particular, by means of simulations with the
FENICIA code, it is shown that the standard features of ITG modes are recovered
with reduced toroidal resolution. Finally, ITG turbulence under the influence
of a static island is studied on the transport timescale with ITER-like
parameters, showing the wide range of applicability of the method
Coma revealed as an extended hard X-rays source by INTEGRAL IBIS/ISGRI
Aims. We report the INTEGRAL/IBIS observations of the Coma Cluster in the
hard X-ray/soft-ray domain. Methods. Since the Coma Cluster appears as an
extended source, its global intensity and significance cannot be directly
extracted with standard coded mask analysis. We used the method of imaging the
extended sources with a coded mask telescope developed by Renaud et al. (2006).
Results. The imaging capabilities and the sensitivity of the IBIS/ISGRI coded
mask instrument allows us to identify for the first time the site of the
emission above ~ 15 keV. We have studied the Coma Cluster morphology in the
18-30keV band and found that it follows the prediction based on X-ray
observations.We also bring constraints on the non-thermal mechanism
contribution at higher energies.Comment: 4 pages, 4 figures, Accepted for publication in A&A Letter
Cosmic Structure Traced by Precision Measurements of the X-Ray Brightest Galaxy Clusters in the Sky
The current status of our efforts to trace cosmic structure with 10^6
galaxies (2MASS), 10^3 galaxy clusters (NORAS II cluster survey), and precision
measurements for 10^2 galaxy clusters (HIFLUGCS) is given. The latter is
illustrated in more detail with results on the gas temperature and metal
abundance structure for 10^0 cluster (A1644) obtained with XMM-Newton.Comment: 4 pages; to be published in the Proceedings of the Conference: The
Emergence of Cosmic Structure, College Park, MD (2002), editors: S.S. Holt
and C. Reynolds; also available at http://www.reiprich.ne
Cosmological Parameters from Observations of Galaxy Clusters
Studies of galaxy clusters have proved crucial in helping to establish the
standard model of cosmology, with a universe dominated by dark matter and dark
energy. A theoretical basis that describes clusters as massive,
multi-component, quasi-equilibrium systems is growing in its capability to
interpret multi-wavelength observations of expanding scope and sensitivity. We
review current cosmological results, including contributions to fundamental
physics, obtained from observations of galaxy clusters. These results are
consistent with and complementary to those from other methods. We highlight
several areas of opportunity for the next few years, and emphasize the need for
accurate modeling of survey selection and sources of systematic error.
Capitalizing on these opportunities will require a multi-wavelength approach
and the application of rigorous statistical frameworks, utilizing the combined
strengths of observers, simulators and theorists.Comment: 53 pages, 21 figures. To appear in Annual Review of Astronomy &
Astrophysic
The origin of the diffuse non-thermal X-ray and radio emission in the Ophiuchus cluster of galaxies
We present high resolution 240 and 607 MHz GMRT radio observations,
complemented with 74 MHz archival VLA radio observations of the Ophiuchus
cluster of galaxies, whose radio mini-halo has been recently detected at 1400
MHz. We also present archival Chandra and XMM-Newton data of the Ophiuchus
cluster. Our observations do not show significant radio emission from the
mini-halo, hence we present upper limits to the integrated, diffuse non-thermal
radio emission of the core of the Ophiuchus cluster. The XMM-Newton
observations can be well explained by a two-temperature thermal model with
temperatures of ~=1.8 keV and ~=9.0 keV, respectively, which confirms previous
results that suggest that the innermost central region of the Ophiuchus cluster
is a cooling core. We also used the XMM-Newton data to set up an upper limit to
the (non-thermal) X-ray emission from the cluster.
The combination of available radio and X-ray data has strong implications for
the currently proposed models of the spectral energy distribution (SED) from
the Ophiuchus cluster. In particular, a synchrotron+IC model is in agreement
with the currently available data, if the average magnetic field is in the
range (0.02-0.3) microG. A pure WIMP annihilation scenario can in principle
reproduce both radio and X-ray emission, but at the expense of postulating very
large boost factors from dark matter substructures, jointly with extremely low
values of the average magnetic field. Finally, a scenario where synchrotron and
inverse Compton emission arise from PeV electron-positron pairs (via
interactions with the CMB), can be ruled out, as it predicts a non-thermal soft
X-ray emission that largely exceeds the thermal Bremsstrahlung measured by
INTEGRAL.Comment: Accepted for publication in MNRAS; 13 pages, 8 figures. Includes
minor changes. Abridged abstrac
An analysis of electron distributions in galaxy clusters by means of the flux ratio of iron lines FeXXV and XXVI
The interpretation of hard X-ray emission from galaxy clusters is still
ambiguous and different models proposed can be probed using various
observational methods. Here we explore a new method based on Fe line
observations.
Spectral line emissivities have usually been calculated for a Maxwellian
electron distribution. In this paper a generalized approach to calculate the
iron line flux for a modified Maxwellian distribution is considered.
We have calculated the flux ratio of iron lines for the various possible
populations of electrons that have been proposed to account for measurements of
hard X-ray excess emission from the clusters A2199 and Coma. We found that the
influence of the suprathermal electron population on the flux ratio is more
prominent in low temperature clusters (as Abell 2199) than in high temperature
clusters (as Coma).Comment: 6 pages, 3 figures, accepted for publication in A&
ROSAT HRI X-ray Observations of the Open Globular Cluster NGC 288
A ROSAT HRI X-ray image was obtained of the open globular cluster NGC 288,
which is located near the South Galactic Pole. This is the first deep X-ray
image of this system. We detect a Low Luminosity Globular Cluster X-ray source
(LLGCX) RXJ005245.0-263449 with an X-ray luminosity of (5.5+-1.4)x10^32 ergs/s
(0.1-2.0 keV), which is located very close to the cluster center. There is
evidence for X-ray variability on a time scale of <~ 1 day. The presence of
this LLGCX in such an open cluster suggests that dense stellar systems with
high interaction rates are not needed to form LLGCXs. We also searched for
diffuse X-ray emission from NGC 288. Upper limits on the X-ray luminosities are
L_X^h < 9.5x10^32 ergs/s (0.52-2.02 keV) and L_X^s < 9.3x10^32 ergs/s
(0.11-0.41 keV). These imply upper limits to the diffuse X-ray to optical light
ratios in NGC 288 which are lower than the values observed for X-ray faint
early-type galaxies. This indicates that the soft X-ray emission in these
galaxies is due either to a component which is not present in globular clusters
(e.g., interstellar gas, or a stellar component which is not found in low
metallicity Population II systems), or to a relatively small number of bright
Low Mass X-ray Binaries (LMXBs).Comment: The Astrophysical Journal in press. Minor revisions to improve
presentation. 6 pages with 3 embedded Postscript figures in emulateapj.st
First Penning-trap mass measurement in the millisecond half-life range: the exotic halo nucleus 11Li
In this letter, we report a new mass for Li using the trapping
experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived
nuclide, , for which a mass measurement has ever been
performed with a Penning trap. Combined with our mass measurements of
Li we derive a new two-neutron separation energy of 369.15(65) keV: a
factor of seven more precise than the best previous value. This new value is a
critical ingredient for the determination of the halo charge radius from
isotope-shift measurements. We also report results from state-of-the-art
atomic-physics calculations using the new mass and extract a new charge radius
for Li. This result is a remarkable confluence of nuclear and atomic
physics.Comment: Formatted for submission to PR
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