1,856 research outputs found
Probing the structure of the cold dark matter halo with ancient mica
Mica can store (for >1 Gy) etchable tracks caused by atoms recoiling from
WIMPs. Ancient mica is a directional detector despite the complex motions it
makes with respect to the WIMP "wind". We can exploit the properties of
directionality and long integration time to probe for structure in the dark
matter halo of our galaxy. We compute a sample of possible signals in mica for
a plausible model of halo structure.Comment: 7 pages, 2 figure
X-ray observations of PKS 0745-191 at the virial radius: Are we there yet?
We wish to reassess the properties of the ICM at large radii in the galaxy
cluster PKS 0745-191 in light of the recent Suzaku measurements. We analyze an
archival 10.5 ksec ROSAT/PSPC observation to extract the surface-brightness
profile of PKS 0745-191 and infer the deprojected density profile. We then
compare the ROSAT surface-brightness profile with the Suzaku result. We perform
a mass analysis combining the ROSAT density profile and the published
temperature profiles from different instruments. We find that the ROSAT
surface-brightness profile is statistically inconsistent (7.7 sigma) with the
Suzaku result around and beyond the value of r200 estimated by Suzaku. We argue
that, thanks to its large field of view and low background, ROSAT/PSPC is to
the present day the most sensitive instrument to low surface-brightness X-ray
emission in the 0.4-2.0 keV band. We also note that the Suzaku temperature and
mass profiles are at odds with the results from at least two other satellites
(XMM-Newton and Swift). The difference in surface brightness between ROSAT and
Suzaku is most likely explained by the existence of additional foreground
components at the low Galactic latitude of the source, which were not taken
into account in the Suzaku background modeling. In light of our mass analysis,
we conclude that any estimate of the fraction of the virial radius reached by
X-ray measures is affected by systematic errors of the order of 25%. As a
result, the properties of the ICM at the virial radius are still uncertain, and
the Suzaku results should be considered with caution.Comment: 6 pages, 5 figures, accepted for publication in A&
OVII and OVIII line emission in the diffuse soft X-ray background: heliospheric and galactic contributions
We study the 0.57 keV (O VII triplet) and 0.65 keV (O VIII) diffuse emission
generated by charge transfer collisions between solar wind (SW) oxygen ions and
interstellar H and He neutral atoms in the inner Heliosphere. These lines which
dominate the 0.3-1.0 keV energy interval are also produced by hot gas in the
galactic halo (GH) and possibly the Local Interstellar Bubble (LB). We
developed a time-dependent model of the SW Charge-Exchange (SWCX) X-ray
emission, based on the localization of the SW Parker spiral at each instant. We
include input SW conditions affecting three selected fields, as well as
shadowing targets observed with XMM-Newton, Chandra and Suzaku and calculate
X-ray emission fot O VII and O VIII lines. We determine SWCX contamination and
residual emission to attribute to the galactic soft X-ray background. We obtain
ground level intensities and/or simulated lightcurves for each target and
compare to X-ray data. The local 3/4 keV emission (O VII and O VIII) detected
in front of shadowing clouds is found to be entirely explained by the CX
heliospheric emission. No emission from the LB is needed at these energies.
Using the model predictions we subtract the heliospheric contribution to the
measured emission and derive the halo contribution. We also correct for an
error in the preliminary analysis of the Hubble Deep Field North (HDFN).Comment: 21 pages (3 on-line), 10 figures (4 on-line), accepted for
publication in Astronomy and Astrophysic
ROSAT PSPC view of the hot interstellar medium of the Magellanic Clouds
Diffuse X-ray emission from the Magellanic Clouds (MCs) is studied by using
all the archival data of pointed ROSAT Position Sensitive Proportional Counter
(PSPC) observations. For this purpose, contributions from the point and
point-like sources in the ROSAT High Resolution Imager (HRI) and PSPC source
catalogues are eliminated and periods of high solar activity are excluded. The
spectral analysis yielded characteristic temperatures of 10^6 - 10^7 K for the
hot thin plasma of the ISM which extends over the whole Large Magellanic Cloud
(LMC) and the Small Magellanic Cloud (SMC). The total unabsorbed luminosity in
the 0.1 - 2.4 keV band within the observed area amounts to 3.2 x 10^38 erg s^-1
in the LMC and 1.1 x 10^37 erg s^-1 in the SMC, each with an uncertainty of
-40%, +100%. The X-ray luminosity of the LMC is comparable to that of other
nearby galaxies with pronounced star formation. In the LMC, hot regions were
found especially around the supergiant shell (SGS) LMC 4 and in the field
covering SGS LMC 2 and LMC 3. Highest temperatures for the SMC were derived in
the southwestern part of the galaxy. The diffuse X-ray emission is most likely
a superposition of the emission from the hot gas in the interior of shells and
supershells as well as from the halo of these galaxies.Comment: accepted by A&
OMCat: Catalogue of Serendipitous Sources Detected with the XMM-Newton Optical Monitor
The Optical Monitor Catalogue of serendipitous sources (OMCat) contains
entries for every source detected in the publicly available XMM-Newton Optical
Monitor (OM) images taken in either the imaging or ``fast'' modes. Since the OM
is coaligned and records data simultaneously with the X-ray telescopes on
XMM-Newton, it typically produces images in one or more near-UV/optical bands
for every pointing of the observatory. As of the beginning of 2006, the public
archive had covered roughly 0.5% of the sky in 2950 fields.
The OMCat is not dominated by sources previously undetected at other
wavelengths; the bulk of objects have optical counterparts. However, the OMCat
can be used to extend optical or X-ray spectral energy distributions for known
objects into the ultraviolet, to study at higher angular resolution objects
detected with GALEX, or to find high-Galactic-latitude objects of interest for
UV spectroscopy.Comment: 25 pages, 22 figures, submitted to PAS
The effect of nucleation of surface slip on the flow and fracture of beryllium final report
Nucleation effect of surface slip on beryllium flow and fractur
Gas temperature profiles in galaxy clusters with Swift XRT: observations and capabilities to map near R200
We investigate the possibility of using the X-ray telescope (XRT) on board
the Swift satellite to improve the current accuracy of the ICM temperature
measurements in the region close to the virial radius of nearby clusters. We
present the spectral analysis of the Swift XRT observations of 6 galaxy
clusters and their temperature profiles in the regions within 0.2-0.6 r200.
Four of them are nearby famous and very well studied objects (Coma, Abell 1795,
Abell 2029 and PKS0745-19). The remaining two, SWJ1557+35 and SWJ0847+13, at
redshift z=0.16 and z=0.36, were serendipitously observed by Swift-XRT. We
accurately quantify the temperature uncertainties, with particular focus on the
impact of the background scatter (both instrumental and cosmic). We extrapolate
these results and simulate a deep observation of the external region of Abell
1795 which is assumed here as a case study. In particular we calculate the
expected uncertainties in the temperature measurement as far as r200. We find
that, with a fairly deep observation (300 ks), the Swift XRT would be able to
measure the ICM temperature profiles in the external regions as far as the
virial radius, significantly improving the best accuracy among the previous
measurements. This can be achieved thanks to the unprecedented combination of
good PSF over the full field of view and very accurate control of the
instrumental background. Somehow unexpectedly we conclude that, among currently
operating telescope, the Swift-XRT is the only potentially able to improve the
current accuracy in plasma temperature measurement at the edges of the cluster
potential. This will be true until a newgeneration of low-background and large
field of view telescopes, aimed to the study of galaxy clusters, will operate.
These observations would be of great importance in developing the observing
strategy for suchmissions.Comment: Accepted for publication in A&A ;13 pages, 13 figure
An XMM-Newton spatially-resolved study of metal abundance evolution in distant galaxy clusters
We present an XMM-Newton analysis of the X-ray spectra of 39 clusters of
galaxies at 0.4<z<1.4, covering a temperature range of 1.5<=kT<=11 keV. We
performed a spatially resolved spectral analysis to study how the abundance
evolves with redshift not only through a single emission measure performed on
the whole cluster but also spatially resolving the cluster emission. We do not
observe a statistically significant (>2sigma) abundance evolution with
redshift. The most significant deviation from no evolution (90% c.l.) is
observed in the emission from the whole cluster (r<0.6r500), that could be
parametrized as Z=A*(1+z)^(-0.8+/-0.5). Dividing the emission in 3 radial bins,
no significant evidence of abundance evolution could be observed fitting the
data with a power-law. A substantial agreement with measures presented in
previous works is found. The error-weighted mean of the spatially resolved
abundances in 3 redshift bins is consistent to be constant with z. Although the
large error bars in the measure of the weighted-mean abundance prevent us from
claiming any significant spatially resolved evolution, the trend with z in the
0.15-0.4r500 radial bin complements nicely the measures of Maughan et al., and
broadly agrees with theoretical predictions. We also found that the data points
derived from the spatially resolved analysis are well fitted by the relation
Z(r,z)=Z0*(1+(r/0.15r500)^2)^(-a)*((1+z)/1.6)^(-gamma), showing a significant
negative trend of Z with the radius and no significant evolution with the
redshift. The present study is the first attempt made to spatially resolve the
evolution of abundance with redshift. However, the sample size and the low
statistics associated with most of the clusters in the sample prevents us to
draw any statistically significant conclusion on the different evolutionary
path that the different regions of the clusters may have traversed.Comment: 12 pages, 8 figures, A&A in press, minor changes (language editing
The gas distribution in the outer regions of galaxy clusters
We present the analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy
clusters with the aim of measuring the density of the X-ray emitting gas in
cluster outskirts. We compare our results with numerical simulations to set
constraints on the azimuthal symmetry and gas clumping in the outer regions of
galaxy clusters. We exploit the large field-of-view and low instrumental
background of ROSAT/PSPC to trace the density of the intracluster gas out to
the virial radius. We perform a stacking of the density profiles to detect a
signal beyond r200 and measure the typical density and scatter in cluster
outskirts. We also compute the azimuthal scatter of the profiles with respect
to the mean value to look for deviations from spherical symmetry. Finally, we
compare our average density and scatter profiles with the results of numerical
simulations. As opposed to some recent Suzaku results, and confirming previous
evidence from ROSAT and Chandra, we observe a steepening of the density
profiles beyond \sim r500. Comparing our density profiles with simulations, we
find that non-radiative runs predict too steep density profiles, whereas runs
including additional physics and/or treating gas clumping are in better
agreement with the observed gas distribution. We report for the first time the
high-confidence detection of a systematic difference between cool-core and
non-cool core clusters beyond \sim 0.3r200, which we explain by a different
distribution of the gas in the two classes. Beyond \sim r500, galaxy clusters
deviate significantly from spherical symmetry, with only little differences
between relaxed and disturbed systems. We find good agreement between the
observed and predicted scatter profiles, but only when the 1% densest clumps
are filtered out in the simulations. [Abridged]Comment: The data for the average profiles and individual clusters can be
downloaded at:
http://www.isdc.unige.ch/~deckert/newsite/The_Planck_ROSAT_project.htm
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