62 research outputs found
Origin of Thermal and Non-Thermal Hard X-ray Emission from the Galactic Center
We analyse new results of Chandra and Suzaku which found a flux of hard X-ray
emission from the compact region around Sgr A (r ~ 100 pc). We suppose
that this emission is generated by accretion processes onto the central
supermassive blackhole when an unbounded part of captured stars obtains an
additional momentum. As a result a flux of subrelativistic protons is generated
near the Galactic center which heats the background plasma up to temperatures
about 6-10 keV and produces by inverse bremsstrahlung a flux of non-thermal
X-ray emission in the energy range above 10 keV.Comment: to be published in PASJ, v.61, No.5, 200
On the lack of strong O-line excess in the Coma cluster outskirts from Suzaku
About half of the baryons in the local Universe are thought to reside in the
so-called warm-hot intergalactic medium (WHIM) at temperatures of 0.1-10
million K. Thermal soft excess emission in the spectrum of some cluster
outskirts that contains OVII and/or OVIII emission lines is regarded as
evidence of the WHIM, although the origin of the lines is controversial due to
strong Galactic and solar system foreground emission. We observed the Coma-11
field, where the most prominent thermal soft excess has ever been reported,
with Suzaku XIS in order to make clear the origin of the excess. We did not
confirm OVII or OVIII excess emission. The OVII and OVIII intensity in Coma-11
is more than 5 sigma below that reported before and we obtained 2 sigma upper
limits of 2.8 and 2.9 photons cm^-2 s^-1 sr^-1 for OVII and OVIII,
respectively. The intensities are consistent with those in another field
(Coma-7) that we measured, and with other measurements in the Coma outskirts
(Coma-7 and X Com fields with XMM-Newton). We did not confirm the spatial
variation within Coma outskirts. The strong oxygen emission lines previously
reported are likely due to solar wind charge exchange.Comment: 5 pages, 3 figures. Accepted for publication in Ap
Fabrication of a 64-Pixel TES Microcalorimeter Array with Iron Absorbers Uniquely Designed for 14.4-keV Solar Axion Search
If a hypothetical elementary particle called an axion exists, to solve the
strong CP problem, a 57Fe nucleus in the solar core could emit a 14.4-keV
monochromatic axion through the M1 transition. If such axions are once more
transformed into photons by a 57Fe absorber, a transition edge sensor (TES)
X-ray microcalorimeter should be able to detect them efficiently. We have
designed and fabricated a dedicated 64-pixel TES array with iron absorbers for
the solar axion search. In order to decrease the effect of iron magnetization
on spectroscopic performance, the iron absorber is placed next to the TES while
maintaining a certain distance. A gold thermal transfer strap connects them. We
have accomplished the electroplating of gold straps with high thermal
conductivity. The residual resistivity ratio (RRR) was over 23, more than eight
times higher than a previous evaporated strap. In addition, we successfully
electroplated pure-iron films of more than a few micrometers in thickness for
absorbers and a fabricated 64-pixel TES calorimeter structure.Comment: 5 pages, 5 figures, published in IEEE Transactions on Applied
Superconductivity on 8 March 202
4 electron temperature driven ultrafast electron localization
Valence transitions in strongly correlated electron systems are caused by
orbital hybridization and Coulomb interactions between localized and
delocalized electrons. The transition can be triggered by changes in the
electronic structure and is sensitive to temperature variations, applications
of magnetic fields, and physical or chemical pressure. Launching the transition
by photoelectric fields can directly excite the electronic states and thus
provides an ideal platform to study the correlation among electrons on
ultrafast timescales. The EuNi(SiGe) mixed-valence
metal is an ideal material to investigate the valence transition of the Eu ions
via the amplified orbital hybridization by the photoelectric field on
sub-picosecond timescales. A direct view on the 4 electron occupancy of the
Eu ions is required to understand the microscopic origin of the transition.
Here we probe the 4 electron states of EuNi(SiGe)
at the sub-ps timescale after photoexcitation by X-ray absorption spectroscopy
across the Eu -absorption edge. The observed spectral changes due to the
excitation indicate a population change of total angular momentum multiplet
states = 0, 1, 2, and 3 of Eu, and the Eu = 7/2 multiplet
state caused by an increase in 4 electron temperature that results in a 4
localization process. This electronic temperature increase combined with
fluence-dependent screening accounts for the strongly non-linear effective
valence change. The data allow us to extract a time-dependent determination of
an effective temperature of the 4 shell, which is also of great relevance in
the understanding of metallic systems' properties, such as the ultrafast
demagnetization of ferromagnetic rare-earth intermetallics and their
all-optical magnetization switching.Comment: 19 pages, 9 figure
Suzaku Observations of the cluster of galaxies Abell 2052
The results from Suzaku XIS observations of the relaxed cluster of galaxies
Abell2052 are presented. Offset pointing data are used to estimate the Galactic
foreground emission in the direction to the cluster. Significant soft X-ray
excess emission above this foreground, the intra-cluster medium emission, and
other background components is confirmed and resolved spectroscopically and
radially. This excess can be described either by (a) local variations of known
Galactic emission components or (b) an additional thermal component with
temperature of about 0.2 keV, possibly associated with the cluster. The radial
temperature and metal abundance profiles of the intra-cluster medium are
measured within \sim 20 in radius (about 60% of the virial radius) from the
cluster center . The temperature drops radially to 0.5-0.6 of the peak value at
a radius of \sim 15'. The gas-mass-weighted metal abundance averaged over the
observed region is found to be 0.21 +- 0.05 times solar.Comment: Accepted for publication in PASJ (2008), 19 pages, postscript figure
Broad-band spectral analysis of the Galactic Ridge X-ray Emission
Detailed spectral analysis of the Galactic X-ray background emission, or the
Galactic Ridge X-ray Emission (GRXE), is presented. To study the origin of the
emission, broad-band and high-quality GRXE spectra were produced from 18
pointing observations with Suzaku in the Galactic bulge region, with the total
exposure of 1 Ms. The spectra were successfully fitted by a sum of two major
spectral components; a spectral model of magnetic accreting white dwarfs with a
mass of 0.66 (0.59-0.75) solar, and a softer optically-thin thermal emission
with a plasma temperature of 1.2-1.5 keV which is attributable to coronal X-ray
sources.
When combined with previous studies which employed high spatial resolution of
the Chandra satellite (e.g. Revnivtsev et al. 2009, Nature), the present
spectroscopic result gives another strong support to a scenario that the GRXE
is essentially an assembly of numerous discrete faint X-ray stars.
The detected GRXE flux in the hard X-ray band was used to estimate the number
density of the unresolved hard X-ray sources. When integrated over a luminosity
range of ~10^30-10^34 erg/s, the result is consistent with a value which was
reported previously by directly resolving faint point sources.Comment: accepted for publication in Ap
Search for Oxygen Emission from Warm-Hot Intergalactic Medium around A2218 with Suzaku
We searched for redshifted O emission lines from the possible warm-hot
intergalactic medium (WHIM) surrounding the cluster of galaxies A2218 at
z=0.1756 using the XIS instrument on Suzaku. This cluster is thought to have an
elongated structure along the line of sight based on previous studies. We
studied systematic uncertainties in the spectrum of the Galactic emission and
in the soft X-ray response of the detectors due to the contamination building
up on the XIS filters. We detected no significant redshifted O lines, and set a
tight constraint on the intensity with upper limits for the surface brightness
of OVII and OVIII lines of 1.1 x 10^-7 and 3.0 x 10^-7 photons cm^-2 s^-1
arcmin^-2, respectively. These upper limits are significantly lower than the
previously reported fluxes from the WHIM around other clusters of galaxies. We
also discuss the prospect for the detection of the WHIM lines with Suzaku XIS
in the future.Comment: 12 pages, 13 figures. Accepted for publication in PASJ Suzaku special
issue (Vol.59, No.SP1
Validation of ozone data from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES)
The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) onboard the International Space Station provided global measurements of ozone profiles in the middle atmosphere from 12 October 2009 to 21 April 2010. We present validation studies of the SMILES version 2.1 ozone product based on coincidence statistics with satellite observations and outputs of chemistry and transport models (CTMs). Comparisons of the stratospheric ozone with correlative data show agreements that are generally within 10%. In the mesosphere, the agreement is also good and better than 30% even at a high altitude of 73km, and the SMILES measurements with their local time coverage also capture the diurnal variability very well. The recommended altitude range for scientific use is from 16 to 73km. We note that the SMILES ozone values for altitude above 26km are smaller than some of the correlative satellite datasets; conversely the SMILES values in the lower stratosphere tend to be larger than correlative data, particularly in the tropics, with less than 8% difference below similar to 24km. The larger values in the lower stratosphere are probably due to departure of retrieval results between two detection bands at altitudes below 28km; it is similar to 3% at 24km and is increasing rapidly down below
The ASTRO-H X-ray Observatory
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly
successful X-ray missions initiated by the Institute of Space and Astronautical
Science (ISAS). ASTRO-H will investigate the physics of the high-energy
universe via a suite of four instruments, covering a very wide energy range,
from 0.3 keV to 600 keV. These instruments include a high-resolution,
high-throughput spectrometer sensitive over 0.3-2 keV with high spectral
resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in
the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers
covering 5-80 keV, located in the focal plane of multilayer-coated, focusing
hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12
keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and
a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the
40-600 keV band. The simultaneous broad bandpass, coupled with high spectral
resolution, will enable the pursuit of a wide variety of important science
themes.Comment: 22 pages, 17 figures, Proceedings of the SPIE Astronomical
Instrumentation "Space Telescopes and Instrumentation 2012: Ultraviolet to
Gamma Ray
The Quiescent Intracluster Medium in the Core of the Perseus Cluster
Clusters of galaxies are the most massive gravitationally-bound objects in
the Universe and are still forming. They are thus important probes of
cosmological parameters and a host of astrophysical processes. Knowledge of the
dynamics of the pervasive hot gas, which dominates in mass over stars in a
cluster, is a crucial missing ingredient. It can enable new insights into
mechanical energy injection by the central supermassive black hole and the use
of hydrostatic equilibrium for the determination of cluster masses. X-rays from
the core of the Perseus cluster are emitted by the 50 million K diffuse hot
plasma filling its gravitational potential well. The Active Galactic Nucleus of
the central galaxy NGC1275 is pumping jetted energy into the surrounding
intracluster medium, creating buoyant bubbles filled with relativistic plasma.
These likely induce motions in the intracluster medium and heat the inner gas
preventing runaway radiative cooling; a process known as Active Galactic
Nucleus Feedback. Here we report on Hitomi X-ray observations of the Perseus
cluster core, which reveal a remarkably quiescent atmosphere where the gas has
a line-of-sight velocity dispersion of 164+/-10 km/s in a region 30-60 kpc from
the central nucleus. A gradient in the line-of-sight velocity of 150+/-70 km/s
is found across the 60 kpc image of the cluster core. Turbulent pressure
support in the gas is 4% or less of the thermodynamic pressure, with large
scale shear at most doubling that estimate. We infer that total cluster masses
determined from hydrostatic equilibrium in the central regions need little
correction for turbulent pressure.Comment: 31 pages, 11 Figs, published in Nature July
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