228 research outputs found
The Chameleonic Contribution to the SZ Radial Profile of the Coma Cluster
We constrain the chameleonic Sunyaev--Zel'dovich (CSZ) effect in the Coma
cluster from measurements of the Coma radial profile presented in the WMAP
7-year results. The CSZ effect arises from the interaction of a scalar (or
pseudoscalar) particle with the cosmic microwave background in the magnetic
field of galaxy clusters. We combine this radial profile data with SZ
measurements towards the centre of the Coma cluster in different frequency
bands, to find Delta T_{SZ,RJ}(0)=-400+/-40 microKelvin and Delta T_{CSZ}^{204
GHz}(0)=-20+/-15 microKelvin (68% CL) for the thermal SZ and CSZ effects in the
cluster respectively. The central value leads to an estimate of the photon to
scalar (or pseudoscalar) coupling strength of g = (5.2 - 23.8) x 10^{-10}
GeV^{-1}, while the 95% confidence bound is estimated to be g < (8.7 - 39.4) x
10^{-10} GeV^{-1}.Comment: 13 pages, 3 figure
Gravitational lensing statistical properties in general FRW cosmologies with dark energy component(s): analytic results
Various astronomical observations have been consistently making a strong case
for the existence of a component of dark energy with negative pressure in the
universe. It is now necessary to take the dark energy component(s) into account
in gravitational lensing statistics and other cosmological tests. By using the
comoving distance we derive analytic but simple expressions for the optical
depth of multiple image, the expected value of image separation and the
probability distribution of image separation caused by an assemble of singular
isothermal spheres in general FRW cosmological models with dark energy
component(s). We also present the kinematical and dynamical properties of these
kinds of cosmological models and calculate the age of the universe and the
distance measures, which are often used in classical cosmological tests. In
some cases we are able to give formulae that are simpler than those found
elsewhere in the literature, which could make the cosmological tests for dark
energy component(s) more convenient.Comment: 14 pages, no figure, Latex fil
SIMBOL-X : a new generation hard X-ray telescope
SIMBOL-X is a hard X-ray mission, operating in the 0.5-70 keV range, which is
proposed by a consortium of European laboratories for a launch around 2010.
Relying on two spacecraft in a formation flying configuration, SIMBOL-X uses a
30 m focal length X-ray mirror to achieve an unprecedented angular resolution
(30 arcsec HEW) and sensitivity (100 times better than INTEGRAL below 50 keV)
in the hard X-ray range. SIMBOL-X will allow to elucidate fundamental questions
in high energy astrophysics, such as the physics of accretion onto Black Holes,
of acceleration in quasar jets and in supernovae remnants, or the nature of the
hard X-ray diffuse emission. The scientific objectives and the baseline
concepts of the mission and hardware design are presented.Comment: 12 pages, 16 fig., Proc. SPIE conf. 5168, San Diego, Aug. 200
Efficacy and safety of statin treatment for cardiovascular disease: a network meta-analysis of 170 255 patients from 76 randomized trials
Background: Statins represent the largest selling class of cardiovascular drug in the world. Previous randomized trials (RCTs) have demonstrated important clinical benefits with statin therapy. Aim: We combined evidence from all RCTs comparing a statin with placebo or usual care among patients with and without prior coronary heart disease (CHD) to determine clinical outcomes. Design: We searched independently, in duplicate, 12 electronic databases (from inception to August 2010), including full text journal content databases, to identify all statin versus inert control RCTs. We included RCTs of any statin versus any non-drug control in any populations. We abstracted data in duplicate on reported major clinical events and adverse events. We performed a random-effects meta-analysis and meta-regression. We performed a mixed treatment comparison using Bayesian methods. Results: We included a total of 76 RCTs involving 170 255 participants. There were a total of 14 878 deaths. Statin therapy reduced all-cause mortality, Relative Risk (RR) 0.90 [95% confidence interval (CI) 0.86-0.94, P ≤ 0.0001, I 2 = 17%]; cardiovascular disease (CVD) mortality (RR 0.80, 95% CI 0.74-0.87, P < 0.0001, I 2 = 27%); fatal myocardial infarction (MI) (RR 0.82, 95% CI 0.75-0.91, P < 0.0001, I 2 = 21%); non-fatal MI (RR 0.74, 95% CI 0.67-0.81, P ≤ 0.001, I 2 = 45%); revascularization (RR 0.76, 95% CI 0.70-0.81, P ≤ 0.0001); and a composite of fatal and non-fatal strokes (0.86, 95% CI 0.78-0.95, P = 0.004, I 2 = 41%). Adverse events were generally mild, but 17 RCTs reported on increased risk of development of incident diabetes [Odds Ratio (OR) 1.09; 95% CI 1.02-1.17, P = 0.001, I 2 = 11%]. Studies did not yield important differences across populations. We did not find any differing treatment effects between statins. Discussion: Statin therapies offer clear benefits across broad populations. As generic formulations become more available efforts to expand access should be a priorit
The X-ray Luminosity Function of Nearby Rich and Poor Clusters of Galaxies: A Cosmological Probe
In this letter, we present a new determination of the local (z<0.09) X-ray
luminosity function (XLF) using a large, statistical sample of 294 Abell
clusters and the ROSAT All-Sky-Survey. Given our large sample size, we have
reduced errors by a factor of two for L(X)(0.5-2keV)>10^43 ergs/sec. We combine
our data with previous work in order to explore possible constraints imposed by
the shape of the XLF on cosmological models. A set of currently viable
cosmologies is used to construct theoretical XLFs assuming Lx is proportional
to M^p and a sigma_8-Omega_0 constraint (from Viana & Liddle 1996) based on the
local X-ray temperature function. We fit these models to our observed XLF and
verify that the simplest adiabatic, analytic scaling relation (e.g. Kaiser
1986) disagrees strongly with observations. If we assume that clusters can be
described by the pre-heated, constant core-entropy models of Evrard & Henry
(1991) then the observed XLF is consistent only with 0.1 < Omega_0 < 0.4 if the
energy per unit mass in galaxies is roughly equal to the gas energy (ie if
beta=1). (abridged)Comment: 4 pages, 2 figures, accepted for publication in ApJ Letters. uses
emulateapj.st
Correlation length of X-ray brightest Abell clusters
We compute the cluster auto-correlation function of an X-ray
flux limited sample of Abell clusters (XBACs, \cite{ebe}). For the total XBACs
sample we find a power-law fit with Mpc
hand consistent with the results of Abell
clusters. We also analyze for subsamples defined by different
X-ray luminosity thresholds where we find a weak tendency of larger values of
with increasing X-ray luminosity although with a low statistical
significance. In the different subsamples analyzed we find Mpc
h and . Our analysis suggests that cluster X-ray
luminosities may be used for a reliable confrontation of cluster spatial
distribution properties in models and observations.Comment: Accepted for publication in Astrophysical Journa
High Momentum Probes of Nuclear Matter
We discuss how the chemical composition of QCD jets is altered by final state
interactions in surrounding nuclear matter. We describe this process through
conversions of leading jet particles. We find that conversions lead to an
enhancement of kaons at high transverse momentum in Au+Au collisions at RHIC,
while their azimuthal asymmetry v_2 is suppressed.Comment: Contribution to the 4th international workshop High-pT physics at LHC
09, Prague; 6 pages, 6 figure
The Kinematics of Intracluster Planetary Nebulae and the On-Going Subcluster Merger in the Coma Cluster Core
The Coma cluster is the richest and most compact of the nearby clusters, yet
there is growing evidence that its formation is still on-going. With a new
multi-slit imaging spectroscopy technique pioneered at the 8.2 m Subaru
telescope and FOCAS, we have detected and measured the line-of-sight velocities
of 37 intracluster planetary nebulae associated with the diffuse stellar
population of stars in the Coma cluster core, at 100 Mpc distance. We detect
clear velocity substructures within a 6 arcmin diameter field. A substructure
is present at ~5000 km/s, probably from in-fall of a galaxy group, while the
main intracluster stellar component is centered around ~6500 km/s, ~700 km/s
offset from the nearby cD galaxy NGC 4874. The kinematics and morphology of the
intracluster stars show that the cluster core is in a highly dynamically
evolving state. In combination with galaxy redshift and X-ray data this argues
strongly that the cluster is currently in the midst of a subcluster merger,
where the NGC 4874 subcluster core may still be self-bound, while the NGC 4889
subcluster core has probably dissolved. The NGC 4889 subcluster is likely to
have fallen into Coma from the eastern A2199 filament, in a direction nearly in
the plane of the sky, meeting the NGC 4874 subcluster arriving from the west.
The two inner subcluster cores are presently beyond their first and second
close passage, during which the elongated distribution of diffuse light has
been created. We predict the kinematic signature expected in this scenario, and
argue that the extended western X-ray arc recently discovered traces the arc
shock generated by the collision between the two subcluster gas halos. Any
preexisting cooling core region would have been heated by the subcluster
collision.Comment: Astronomy & Astrophysics, in press, 9 pages, 5 figure
Galaxy Clusters in the Swift/BAT era II: 10 more Clusters detected above 15 keV
We report on the discovery of 10 additional galaxy clusters detected in the
ongoing Swift/BAT all-sky survey. Among the newly BAT-discovered clusters there
are: Bullet, Abell 85, Norma, and PKS 0745-19. Norma is the only cluster, among
those presented here, which is resolved by BAT. For all the clusters we perform
a detailed spectral analysis using XMM-Newton and Swift/BAT data to investigate
the presence of a hard (non-thermal) X-ray excess. We find that in most cases
the clusters' emission in the 0.3-200keV band can be explained by a
multi-temperature thermal model confirming our previous results. For two
clusters (Bullet and Abell 3667) we find evidence for the presence of a hard
X-ray excess. In the case of the Bullet cluster, our analysis confirms the
presence of a non-thermal, power-law like, component with a 20-100 keV flux of
3.4 \times 10-12 erg cm-2 s-1 as detected in previous studies. For Abell 3667
the excess emission can be successfully modeled as a hot component (kT=~13keV).
We thus conclude that the hard X-ray emission from galaxy clusters (except the
Bullet) has most likely thermal origin.Comment: Accepted for publication by Ap
Restrictions on parameters of sterile neutrino dark matter from observations of galaxy clusters
We find restrictions on the mass and mixing angle of the dark matter sterile
neutrinos using X-ray observations of Coma and Virgo galaxy clusters.Comment: 10 page
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