1,787 research outputs found
DIOS: the dark baryon exploring mission
DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small satellite aiming for
a launch around 2020 with JAXA's Epsilon rocket. Its main aim is a search for
warm-hot intergalactic medium with high-resolution X-ray spectroscopy of
redshifted emission lines from OVII and OVIII ions. The superior energy
resolution of TES microcalorimeters combined with a very wide field of view
(30--50 arcmin diameter) will enable us to look into gas dynamics of cosmic
plasmas in a wide range of spatial scales from Earth's magnetosphere to
unvirialized regions of clusters of galaxies. Mechanical and thermal design of
the spacecraft and development of the TES calorimeter system are described. We
also consider revising the payload design to optimize the scientific capability
allowed by the boundary conditions of the small mission.Comment: 10 pages, 11 figures, Proceedings of the SPIE Astronomical
Instrumentation : Space Telescopes and Instrumentation 2014: Ultraviolet to
Gamma Ra
Gas, Iron and Gravitational Mass in Galaxy Clusters: The General Lack of Cluster Evolution at z < 1.0
We have analyzed the ASCA data of 29 nearby clusters of galaxies
systematically, and obtained temperatures, iron abundances, and X-ray
luminosities of their intracluster medium (ICM). We also estimate ICM mass
using the beta model, and then evaluate iron mass contained in the ICM and
derive the total gravitating mass. This gives the largest and most homogeneous
information about the ICM derived only by the ASCA data. We compare these
values with those of distant clusters whose temperatures, abundances, and
luminosities were also measured with ASCA, and find no clear evidence of
evolution for the clusters at z<1.0. Only the most distant cluster at z=1.0,
AXJ2019.3+1127, has anomalously high iron abundance, but its iron mass in the
ICM may be among normal values for the other clusters, because the ICM mass may
be smaller than the other clusters. This may suggest a hint of evolution of
clusters at z ~ 1.0.Comment: 23 pages including 5 figures. Using PASJ2.sty, and PASJ95.sty.
Accepted by PAS
X-ray emission from thin plasmas. Collisional ionization for atoms and ions of H to Zn
Every observation of astrophysical objects involving a spectrum requires
atomic data for the interpretation of line fluxes, line ratios and ionization
state of the emitting plasma. One of the processes which determines it is
collisional ionization. In this study an update of the direct ionization (DI)
and excitation-autoionization (EA) processes is discussed for the H to Zn-like
isoelectronic sequences. In the last years new laboratory measurements and
theoretical calculations of ionization cross sections have become available. We
provide an extension and update of previous published reviews in the
literature. We include the most recent experimental measurements and fit the
cross sections of all individual shells of all ions from H to Zn. These data
are described using an extension of Younger's and Mewe's formula, suitable for
integration over a Maxwellian velocity distribution to derive the subshell
ionization rate coefficients. These ionization rate coefficients are
incorporated in the high-resolution plasma code and spectral fitting tool SPEX
V3.0.Comment: Accepted for publication in A&A, 22 pages, 18 figure
Relativistic Corrections to the Sunyaev-Zel'dovich Effect for Clusters of Galaxies. IV. Analytic fitting formula for the Numerical Results
We present an accurate analytic fitting formula for the numerical results for
the relativistic corrections to the thermal Sunyaev-Zel'dovich effect for
clusters of galaxies. The numerical results for the relativistic corrections
have been obtained by numerical integration of the collision term of the
Boltzmann equation. The fitting is carried out for the ranges 0.02 < theta_{e}
< 0.05 and 0 < X < 20, where theta_{e} = k_{B}T_{e}/m_{e}c^{2}, X =
omega/k_{B}T_{0}, T_{e} is the electron temperature, omega is the angular
frequency of the photon, and T_{0} is the temperature of the cosmic microwave
background radiation. The accuracy of the fitting is generally better than
0.1%. The present analytic fitting formula will be useful for the analyses of
the thermal Sunyaev-Zel'dovich effect for high-temperature galaxy clusters.Comment: 11 pages + 1 table + 2 figures, LaTeX with AASMS macro. Accepted by
Astrophysical Journal for publicatio
Investigation of slow collisions for (quasi) symmetric heavy systems: what can be extracted from high resolution X-ray spectra
We present a new experiment on (quasi) symmetric collision systems at
low-velocity, namely Ar ions ( a.u.) on gaseous Ar and N
targets, using low- and high-resolution X-ray spectroscopy. Thanks to an
accurate efficiency calibration of the spectrometers, we extract absolute X-ray
emission cross sections combining low-resolution X-ray spectroscopy and a
complete determination of the ion beam - gas jet target overlap. Values with
improved uncertainty are found in agreement with previous results
\cite{Tawara2001}. Resolving the whole He-like Ar Lyman series from
to 10 with our crystal spectrometer enables to determine precisely the
distribution of the electron capture probability and the
preferential level of the selective single-electron capture.
Evaluation of cross sections for this process as well as for the contribution
of multiple-capture is carried out. Their sensitivity to the
-distribution of levels populated by single-electron capture is
clearly demonstrated, providing a stringent benchmark for theories. In
addition, the hardness ratio is extracted and the influence of the decay of the
metastable state on this ratio is discussed
A Hot Spot in Coma
We study the temperature structure of the central part (r<18' ~0.7 h50**-1
Mpc) of the Coma cluster of galaxies using ASCA data. Two different analysis
methods produce results in good agreement with each other and reveal the
presence of interesting structures in the gas temperature distribution.
Globally, the average temperature in the center of the cluster is 9.0 +/- 0.6
keV in good agreement with previous results. Superimposed on this, we find a
cool area with temperatures of 4-6 keV associated with a filament of X-ray
emission extending southeast from the cluster center detected by Vikhlinin and
coworkers. We also find a hot spot with a temperature of around 13 keV
displaced north from the central peak of emission. The distribution of the gas
temperatures and relative specific entropies suggests that the cool features
are most likely gas stripped from a galaxy group centered on NGC 4874 falling
toward the core from outside, while the hot spot located ``ahead'' of this
in-falling gas is due to shock heating. Thus our results suggest that we are
observing Coma during a minor merger with a small group of galaxies associated
with NGC 4874 shortly before the initial core passage.Comment: 5 pages, 2 figures, accepted for publication in the Astrophysical
Journa
How Abundant is Iron in the Core of the Perseus Cluster?
The analysis of Perseus data collected with the Medium Energy Concentrator
Spectrometer (MECS) on board Beppo-SAX shows that the ratio of the flux of the
8 keV line complex (dominated by Fe K emission) over the 6.8 keV line
complex (dominated by Fe K emission) is significantly larger than
predicted by standard thermal emission codes. Moreover the analysis of
spatially resolved spectra shows that the above ratio decreases with increasing
cluster radius. We find that, amongst the various explanations we consider, the
most likely requires the plasma to be optically thick for resonant scattering
at the energy of the Fe K line. We argue that if this is the case,
then measures of the iron abundance made using standard thermal emission codes,
that assume optically thin emission, can significantly underestimate the true
iron abundance. In the case of the core of Perseus we estimate the true
abundance to be 0.9 solar in a circular region with radius of
kpc and centered on NGC 1275. Finally we speculate that similar results may
hold for the core of other rich clusters.Comment: 19 pages, 3 Postscript figure
DIOS: the Diffuse Intergalactic Oxygen Surveyor
We present our proposal for a small X-ray mission DIOS (Diffuse Intergalactic
Oxygen Surveyor), consisting of a 4-stage X-ray telescope and an array of TES
microcalorimeters, cooled with mechanical coolers, with a total weight of about
400 kg. The mission will perform survey observations of warm-hot intergalactic
medium using OVII and OVIII emission lines, with the energy coverage up to 1.5
keV. The wide field of view of about 50' diameter, superior energy resolution
close to 2 eV FWHM, and very low background will together enable us a wide
range of science for diffuse X-ray sources. We briefly describe the design of
the satellite, performance of the subsystems and the expected results.Comment: 9 pages, 11 figures, a proceedings of SPIE "Astronomical Telescopes
and Instrumentation" 200
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