61 research outputs found
X-Ray Reflection Nebulae with Large Equivalent Widths of Neutral Iron Ka Line in the Sgr C Region
This paper reports on the first results of the Suzaku observation in the Sgr
C region. We detected four diffuse clumps with strong line emission at 6.4keV,
Ka from neutral or low-ionized Fe. One of them, M359.38-0.00, is newly
discovered with Suzaku. The X-ray spectra of the two bright clumps,
M359.43-0.07 and M359.47-0.15, after subtracting the Galactic center diffuse
X-ray emission (GCDX), exhibit strong Ka line from FeI with large equivalent
widths (EWs) of 2.0-2.2keV and clear Kb of FeI. The GCDX in the Sgr C region is
composed of the 6.4keV- and 6.7keV-associated components. These are
phenomenologically decomposed by taking relations between EWs of the 6.4keV and
6.7keV lines. Then the former EWs against the associated continuum in the
bright clump regions are estimated to be 2.4(+2.3_-0.7)keV. Since the two
different approaches give similar large EWs of 2keV, we strongly suggest that
the 6.4keV clumps in the Sgr C region are due to X-ray reflection/fluorescence
(the X-ray reflection nebulae).Comment: Accepted for publication in PAS
Electrochemical Capacitors Using Fluorohydrogenate Ionic Liquid Electrolytes
Electrochemical capacitors using fluorohydrogenate ionic liquids show a large voltage dependence of capacitance with a maximum at a charging voltage around 2.5 V, resulting in a larger capacitance than those using other typical ionic liquid electrolytes. The voltage dependence becomes less remarkable with decrease in the HF composition n in EMIm(FH)nF (EMIm: 1-ethyl-3-methylimidazolium). Cyclic voltammetry using an activated carbon working electrode revealed that two redox reactions occur at the higher and lower potentials against the rest potential in EMIm(FH)2.3F. These Faradaic processes contribute to the voltage dependence of capacitance
Spectral transitions of an ultraluminous X-ray source, NGC 2403 Source 3
Suzaku observation of an ultraluminous X-ray source, NGC 2403 Source 3,
performed on 2006 March 16--17, is reported. The Suzaku XIS spectrum of Source
3 was described with a multi-color black-body-like emission from an optically
thick accretion disk. The innermost temperature and radius of the accretion
disk was measured to be keV and km, respectively, where with being the disk inclination. The bolometric
luminosity of the source was estimated to be ergs s. Archival Chandra and XMM-Newton data of the source were
analyzed for long-term spectral variations. In almost all observations, the
source showed multi-color black-body-like X-ray spectra with parameters similar
to those in the Suzaku observation. In only one Chandra observation, however,
Source 3 was found to exhibit a power-law-like spectrum, with a photon index of
, when it was fainter by about than in the
Suzaku observation. The spectral behavior is naturally explained in terms of a
transition between the slim disk state and the "very high" states, both found
in Galactic black hole binaries when their luminosity approach the Eddington
limit. These results are utilized to argue that ultraluminous X-ray sources
generally have significantly higher black-hole masses than ordinary
stellar-mass black holes.Comment: Accepted for PASJ 3nd Suzaku special issu
Talonavicular joint abnormalities and walking ability of patients with rheumatoid arthritis.
Rheumatoid arthritis (RA) is often associated with deformities of the feet, and foot pain often arises in the talonavicular joint of patients with RA. The object of this study was to assess the relationship between magnetic resonance imaging (MRI) findings of the talonavicular joint and walking ability. The subjects were 35 RA patients (10 feet in 5 males and 56 feet in 30 females) aged 34-87 years (mean: 70 years +/- 12.1), with a disease duration from 1-54 years (mean: 14 years +/- 12.1). MRI findings were classified as follows: Grade 1, almost normal; Grade 2, early articular destruction; Grade 3, moderate articular destruction; Grade 4, severe articular destruction; and Grade 5, bony ankylosis dislocation. Walking ability was classified into one of 9 categories ranging from normal gait to bedridden status according to the system of Fujibayashi. As the grade of MRI images became higher the walking ability decreased, and these parameters showed a correlation by Spearman's rank correlation coefficient analysis (P = 0.003). Thus, in the present cohort group of patients with RA, the deterioration of walking ability increased with the severity of destruction of the talonavicular joint.</p
Unusual diffuse X-ray source in the Galactic center region
We report the ASCA and Chandra discovery of a diffuse X-ray source in the
Galactic center region. The X-ray spectrum is fitted with a non-equilibrium
ionization (NEI) plasma model of about 6-keV temperature. The model requires
higher than solar metal abundances, a young plasma age of 100 years
and a large N_H value of about 10^{23} cm^{-2}. The N_H value constrains the
source position to be in the Galactic center region at about 8.5 kpc distance.
The high resolution X-ray image with the Chandra ACIS shows a ring of 10''
radius which corresponds to 0.4 pc at the Galactic center, and a tail-like
structure. Although the morphology is peculiar, the other X-ray features are
likely to be a very young supernova remnant, possibly in a free expansion
phase.Comment: 11 pages, 4 figures, to be published in Ap
Suzaku Detection of Extended/Diffuse Hard X-Ray Emission from the Galactic Center
Five on-plane regions within +/- 0.8deg of the Galactic center were observed
with the Hard X-ray Detector (HXD) and the X-ray Imaging Spectrometer (XIS)
onboard Suzaku. From all regions, significant hard X-ray emission was detected
with HXD-PIN up to 40 keV, in addition to the extended plasma emission which is
dominant in the XIS band. The hard X-ray signals are inferred to come primarily
from a spatially extended source, rather than from a small number of bright
discrete objects. Contributions to the HXD data from catalogued X-ray sources,
typically brighter than 1 mCrab, were estimated and removed using information
from Suzaku and other satellites. Even after this removal, the hard X-ray
signals remained significant, exhibiting a typical 12--40 keV surface
brightness of 4E-10 erg cm-2 s-1 deg-2 and power-law-like spectra with a photon
index of 1.8. Combined fittings to the XIS and HXD-PIN spectra confirm that a
separate hard tail component is superposed onto the hot thermal emission,
confirming a previous report based on the XIS data. Over the 5--40 keV band,
the hard tail is spectrally approximated by a power law of photon index ~2, but
better by those with somewhat convex shapes. Possible origins of the extended
hard X-ray emission are discussed.Comment: 13 pages, 18 figure
Iron and Nickel Line Diagnostics for the Galactic Center Diffuse Emission
We have observed the diffuse X-ray emission from the Galactic center (GC)
using the X-ray Imaging Spectrometer (XIS) on Suzaku. The high-energy
resolution and the low-background orbit provide excellent spectra of the GC
diffuse X-rays (GCDX). The XIS found many emission lines in the GCDX near the
energy of K-shell transitions of iron and nickel. The most pronounced features
are FeI K alpha at 6.4 keV and K-shell absorption edge at 7.1 keV, which are
from neutral and/or low ionization states of iron, and the K-shell lines at 6.7
keV and 6.9 keV from He-like (FeXXV K alpha) and hydrogenic (FeXXVI Ly alpha)
ions of iron. In addition, K alpha lines from neutral or low ionization nickel
(NiI K alpha) and He-like nickel (NiXXVII K alpha), and FeI K beta, FeXXV K
beta, FeXXVI Ly beta, FeXXV K gamma and FeXXVI Ly gamma are detected for the
first time. The line center energies and widths of FeXXV K alpha and FeXXVI Ly
alpha favor a collisional excitation (CE) plasma for the origin of the GCDX.
The electron temperature determined from the line flux ratio of FeXXV K alpha /
FeXXV K beta is similar to the ionization temperature determined from that of
FeXXV K alpha /FeXXVI Ly alpha. Thus it would appear that the GCDX plasma is
close to ionization equilibrium. The 6.7 keV flux and temperature distribution
to the galactic longitude is smooth and monotonic,in contrast to the integrated
point source flux distribution. These facts support the hypothesis that the
GCDX is truly diffuse emission rather than the integration of the outputs of a
large number of unresolved point sources. In addition, our results demonstrate
that the chemical composition of Fe in the interstellar gas near the GC is
constrained to be about 3.5 times solar.Comment: 11 pages, 19 figures. Accepted for publication in PASJ Suzaku Special
Issue (vol. 59 sp. 1
Suzaku Observation of the Metallicity in the Interstellar Medium of NGC 4258
The Suzaku X-ray satellite observed the nearby spiral galaxy NGC 4258 for a
total good exposure time of 100 ks. We present an analysis of the Suzaku XIS
data, in which we confirm that the 0.5--2 keV spectra of the interstellar
medium (ISM) are well-represented by a two-temperature model. The cool and hot
ISM temperatures are 0.23+-0.02 and 0.59 +-0.01 keV, respectively. Suzaku's
excellent spectral sensitivity enables us to measure the metal abundances of O,
Ne, Mg, Si and Fe of the ISM for the first time. The resultant abundance
pattern of O, Mg, Si, and Fe is consistent with that of the new solar abundance
table of Lodders (2003), rather than Anders & Grevesse (1989). This suggests
that the metal enrichment processes of NGC 4258 and of our Galaxy are similar.Comment: 9 pages, 4 figure
Discovery of a possible X-ray counterpart to HESS J1804-216
Suzaku deep observations have discovered two highly significant nonthermal
X-ray sources, Suzaku J18042142 (Src 1) and Suzaku J18042140 (Src 2),
positionally coincident with the unidentified TeV -ray source, HESS
J1804216. The X-ray sources are not time variable and show no counterpart in
other wavebands, except for the TeV source. Src 1 is unresolved at Suzaku
spatial resolution, whereas Src 2 is extended or composed of multiple sources.
The X-ray spectra are highly absorbed, hard, and featureless, and are well
fitted by absorbed power-law models with best-fit photon indices and absorption
columns of and cm
for Src 1, and and
cm for Src 2. The measured X-ray absorption to the latter source is
significantly larger than the total Galactic neutral hydrogen column in that
direction. The unabsorbed 2--10 keV band luminosities are ergs s (Src 1) and ergs s (Src 2), where is the source distance. Among the
handful of TeV sources with known X-ray counterparts, HESS J1804216 has the
largest ratio of TeV -ray to hard X-ray fluxes. We discuss the nature
of the emission and propose the Suzaku sources as plausible counterparts to the
TeV source, although further observations are necessary to confirm this.Comment: 12 pages, 5 figures, Publications of the Astronomical Society of
Japan, in pres
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