6,679 research outputs found
Confirming the Detection of an Intergalactic X-ray Absorber Toward PKS 2155-304
We present new observations on PKS 2155-304 with the Chandra Low Energy
Transmission Grating Spectrometer (LETG), using the Advanced CCD Imaging
Spectrometer (ACIS). We confirm the detection of an absorption line plausibly
identified as OVIII Ly-alpha from the warm-hot intergalactic medium associated
with a small group of galaxies along the line of sight, as originally reported
by Fang et al. 2002 (here after FANG02). Combining the previous observations in
FANG02 and five new, long observations on the same target, we increase the
total exposure time by a factor of three, and the total counts per resolution
element by a factor of five. The measured line equivalent width is smaller than
that observed in FANG02, but still consistent at 90% confidence. We also
analyze the XMM-Newton observations on the same target, as well as observations
using the Chandra LETG and the High Resolution Camera (HRC) combination. These
observations have been used to challenge our reported detection. While no line
is seen in either the XMM-Newton and the Chandra LETG+HRC data, we find that
our result is consistent with the upper limits from both data sets. We
attribute the non-detection to (1) higher quality of the Chandra LETG+ACIS
spectrum, and (2) the rather extended wings of the line spread functions of
both the XMM RGS and the Chandra LETG+HRC. We discuss the implication of our
observation on the temperature and density of the absorber. We also confirm the
detection of z ~ 0 OVII absorption and, comparing with previous Chandra
analysis, we obtain much tighter constraints on the line properties.Comment: 10 pages, 8 figures, accepted for publication in Ap
X-Ray Emission from the Warm Hot Intergalactic Medium
The number of detected baryons in the Universe at z<0.5 is much smaller than
predicted by standard big bang nucleosynthesis and by the detailed observation
of the Lyman alpha forest at red-shift z=2. Hydrodynamical simulations indicate
that a large fraction of the baryons today is expected to be in a ``warm-hot''
(10^5-10^7K) filamentary gas, distributed in the intergalactic medium. This
gas, if it exists, should be observable only in the soft X-ray and UV bands.
Using the predictions of a particular hydrodynamic model, we simulated the
expected X-ray flux as a function of energy in the 0.1-2 keV band due to the
Warm-Hot Intergalactic Medium (WHIM), and compared it with the flux from local
and high red-shift diffuse components. Our results show that as much as 20% of
the total diffuse X-ray background (DXB) in the energy range 0.37-0.925keV
could be due to X-ray flux from the WHIM, 70% of which comes from filaments at
redshift z between 0.1 and 0.6. Simulations done using a FOV of 3', comparable
with that of Suzaku and Constellation-X, show that in more than 20% of the
observations we expect the WHIM flux to contribute to more than 20% of the DXB.
These simulations also show that in about 10% of all the observations a single
bright filament in the FOV accounts, alone, for more than 20% of the DXB flux.
Red-shifted oxygen lines should be clearly visible in these observations.Comment: 19 pages, 6 figure
On polymorphic logical gates in sub-excitable chemical medium
In a sub-excitable light-sensitive Belousov-Zhabotinsky chemical medium an
asymmetric disturbance causes the formation of localized traveling
wave-fragments. Under the right conditions these wave-fragment can conserve
their shape and velocity vectors for extended time periods. The size and life
span of a fragment depend on the illumination level of the medium. When two or
more wave-fragments collide they annihilate or merge into a new wave-fragment.
In computer simulations based on the Oregonator model we demonstrate that the
outcomes of inter-fragment collisions can be controlled by varying the
illumination level applied to the medium. We interpret these wave-fragments as
values of Boolean variables and design collision-based polymorphic logical
gates. The gate implements operation XNOR for low illumination, and it acts as
NOR gate for high illumination. As a NOR gate is a universal gate then we are
able to demonstrate that a simulated light sensitive BZ medium exhibits
computational universality
On the dynamical structure of the Trojan group of asteroids
Using a semi-analytical approach, domains of possible motion for Trojan asteroids were established. It is shown that stable librating motion is possible for both high inclination and high eccentricity. Frequency distributions were also produced for real Trojan asteroids, against differing libration amplitudes and libration periods
Cosmological SPH simulations with four million particles: statistical properties of X-ray clusters in a low-density universe
We present results from a series of cosmological SPH (smoothed particle
hydrodynamics) simulations coupled with the P3M
(Particle-Particle-Particle-Mesh) solver for the gravitational force. The
simulations are designed to predict the statistical properties of X-ray
clusters of galaxies as well as to study the formation of galaxies. We have
seven simulation runs with different assumptions on the thermal state of the
intracluster gas. Following the recent work by Pearce et al., we modify our SPH
algorithm so as to phenomenologically incorporate the galaxy formation by
decoupling the cooled gas particles from the hot gas particles. All the
simulations employ 128^3 particles both for dark matter and for gas components,
and thus constitute the largest systematic catalogues of simulated clusters in
the SPH method performed so far. These enable us to compare the analytical
predictions on statistical properties of X-ray clusters against our direct
simulation results in an unbiased manner. We find that the luminosities of the
simulated clusters are quite sensitive to the thermal history and also to the
numerical resolution of the simulations, and thus are not reliable. On the
other hand, the mass-temperature relation for the simulated clusters is fairly
insensitive to the assumptions of the thermal state of the intracluster gas,
robust against the numerical resolution, and in fact agrees well with the
analytic prediction. Therefore the prediction for the X-ray temperature
function of clusters on the basis of the Press-Schechter mass function and the
virial equilibrium is fairly reliable.Comment: Accepted for publication in The Astrophysical Journal. 18 pages with
7 embedded figure
Submillimeter detection of the Sunyaev -- Zel'dovich effect toward the most luminous X-ray cluster at z=0.45
We report on the detection of the Sunyaev -- Zel'dovich (SZ) signals toward
the most luminous X-ray cluster RXJ1347-1145 at Nobeyama Radio Observatory (21
and 43 GHz) and at James Clerk Maxwell Telescope (350 GHz). In particular the
latter is the first successful detection of the SZ temperature increment in the
submillimeter band which resolved the profile of a cluster of galaxies. Both
the observed spectral dependence and the radial profile of the SZ signals are
fully consistent with those expected from the X-ray observation of the cluster.
The combined analysis of 21GHz and 350GHz data reproduces the temperature and
core-radius of the cluster determined with the ROSAT and ASCA satellites when
we adopt the slope of the density profile from the X-ray observations.
Therefore our present data provide the strongest and most convincing case for
the detection of the submillimeter SZ signal from the cluster, as well as in
the Rayleigh -- Jeans regime. We also discuss briefly the cosmological
implications of the present results.Comment: 11 pages, The Astrophysical Journal (Letters), in pres
Quantum mode filtering of non-Gaussian states for teleportation-based quantum information processing
We propose and demonstrate an effective mode-filtering technique of
non-Gaussian states generated by photon-subtraction. More robust non-Gaussian
states have been obtained by removing noisy low frequencies from the original
mode spectrum. We show that non-Gaussian states preserve their non-classicality
after quantum teleportation to a higher degree, when they have been
mode-filtered. This is indicated by a stronger negativity of
the Wigner function at the origin, compared to for states
that have not been mode-filtered. This technique can be straightforwardly
applied to various kinds of photon-subtraction protocols, and can be a key
ingredient in a variety of applications of non-Gaussian states, especially
teleportation-based protocols towards universal quantum information processing
Energy Loss Function and Source Function for Au 4f Photoelectrons Derived by Monte Carlo Analysis of Reflection Electron Energy Loss Spectroscopy (REELS) and X-Ray Photoelectron Spectroscopy (XPS) Spectra
We have derived the energy loss function of Au for 1 keV electrons by Monte Carlo analysis of the reflection electron energy loss spectroscopy (REELS) spectra. This energy loss function was significantly different from the optical loss function widely used and has revealed that the surface excitation affects the energy loss spectrum of keV electrons.
X-ray photoelectron spectroscopy (XPS) background subtraction has been recently developed by using the energy loss function derived from the transmission electron energy loss spectroscopy (TEELS). We have demonstrated that the energy loss function derived from REELS has enabled a more accurate Au 4f XPS spectrum to be obtained after subtraction of the inelastic background
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