521 research outputs found
Suzaku investigation into the nature of the nearest ultraluminous X-ray source, M33 X-8
The X-ray spectrum of the nearest ultraluminous X-ray source, M33 X-8,
obtained by Suzaku during 2010 January 11 -- 13, was closely analyzed to
examine its nature. It is, by far, the only data with the highest signal
statistic in 0.4 -- 10 keV range. Despite being able to reproduce the X-ray
spectrum, Comptonization of the disk photons failed to give a physically
meaningful solution. A modified version of the multi-color disk model, in which
the dependence of the disk temperature on the radius is described as r^(-p)
with p being a free parameter, can also approximate the spectrum. From this
model, the innermost disk temperature and bolometric luminosity were obtained
as T_in = 2.00-0.05+0.06 keV and L_disk = 1.36 x 10^39 (cos i)^(-1) ergs/s,
respectively, where i is the disk inclination. A small temperature gradient of
p = 0.535-0.005+0.004, together with the high disk temperature, is regarded as
the signatures of the slim accretion disk model, suggesting that M33 X-8 was
accreting at high mass accretion rate. With a correction factor for the slim
disk taken into account, the innermost disk radius, R_in =81.9-6.5+5.9 (cos
i)^(-0.5) km, corresponds to the black hole mass of M \sim 10 M_sun (cos
i)^(-0.5). Accordingly, the bolometric disk luminosity is estimated to be about
80 (cos i)^(-0.5)% of the Eddington limit. A numerically calculated slim disk
spectrum was found to reach a similar result. Thus, the extremely
super-Eddington luminosity is not required to explain the nature of M33 X-8.
This conclusion is utilized to argue for the existence of intermediate mass
black holes with M > 100 M_sun radiating at the sub/trans-Eddington luminosity,
among ultraluminous X-ray sources with L_disk > 10^(40) ergs/s.Comment: 10 pages, 4 figures, PASJ accepte
Relict minerals and their assemblages in Yamato-691 (EH3)
Four relict minerals; olivine, pyroxene, a silica mineral and metallic (Fe, Ni) were found in the chondrules and as the mineral fragments of Yamato-691 (EH3). Two mineral assemblages of the relict minerals were found; (a) olivine+pyroxene+metallic (Fe, Ni), and (b) pyroxene+silica mineral. The relict pyroxene in assemblage (a) was formed from the reaction of olivine and silica-rich phase (gas or liquid). These two assemblages cannot coexist under an equilibrium condition. The compositional difference of pyroxene between assemblages (a) and (b) suggests the fractionation which occurred before the chondrule formation
Similarities of artificial photosystems by ruthenium oxo complexes and native water splitting systems.
The nature of chemical bonds of ruthenium(Ru)-quinine(Q) complexes, mononuclear [Ru(trpy)(3, 5-t-Bu(2)Q)(OH(2))](ClO(4))(2) (trpy = 2, 2('):6('), 2('')-terpyridine, 3, 5-di-tert-butyl-1, 2-benzoquinone) (1), and binuclear [Ru(2)(btpyan)(3, 6-di-Bu(2)Q)(2)(OH(2))](2+) (btpyan = 1, 8-bis(2, 2('):6('), 2('')-terpyrid-4(')-yl)anthracene, 3, 6-t-Bu(2)Q = 3, 6-di-tert-butyl-1, 2-benzoquinone) (2), has been investigated by broken-symmetry (BS) hybrid density functional (DFT) methods. BS DFT computations for the Ru complexes have elucidated that the closed-shell structure (2b) Ru(II)-Q complex is less stable than the open-shell structure (2bb) consisting of Ru(III) and semiquinone (SQ) radical fragments. These computations have also elucidated eight different electronic and spin structures of tetraradical intermediates that may be generated in the course of water splitting reaction. The Heisenberg spin Hamiltonian model for these species has been derived to elucidate six different effective exchange interactions (J) for four spin systems. Six J values have been determined using total energies of the eight (or seven) BS solutions for different spin configurations. The natural orbital analyses of these BS DFT solutions have also been performed in order to obtain natural orbitals and their occupation numbers, which are useful for the lucid understanding of the nature of chemical bonds of the Ru complexes. Implications of the computational results are discussed in relation to the proposed reaction mechanisms of water splitting reaction in artificial photosynthesis systems and the similarity between artificial and native water splitting systems
Suzaku observation of the giant radio galaxy 3C 326
A Suzaku observation of a giant radio galaxy, 3C 326, which has a physical
size of about 2 Mpc, was conducted on 2008 January 19 -- 21. In addition to
several X-ray sources, diffuse emission was significantly detected associated
with its west lobe, but the east lobe was contaminated by an unidentified X-ray
source WARP J1552.4+2007. After careful evaluation of the X-ray and Non X-ray
background, the 0.4 -- 7 keV X-ray spectrum of the west lobe is described by a
power-law model. The photon index and 1 keV flux density was derived as
and nJy,
respectively, where the first and second errors represent the statistical and
systematic ones. The diffuse X-rays were attributed to be inverse Compton
radiation by the synchrotron radio electrons scattering off the cosmic
microwave background photons. This radio galaxy is the largest among those with
lobes detected through inverse Compton X-ray emission. A comparison of the
radio to X-ray fluxes yields the energy densities of electron and magnetic
field as ergs/cm3 and ergs/cm3, respectively. The galaxy
is suggested to host a low luminosity nucleus with an absorption-corrected 2 --
10 keV luminosity of ergs/s, together with a relatively
weak radio core. The energetics in the west lobe of 3C 326 were compared with
those of moderate radio galaxies with a size of kpc. The west lobe
of 3C 326 is confirmed to agree with the correlations for the moderate radio
galaxies, and , where
is their total physical size. This implies that the lobes of 3C 326 are
still being energized by the jet, despite the current weakness of the nucleus.Comment: 11 pages, 10 figures, 6 tables, Accepted for ApJ (v706 issue
Nihon University CubeSat Program
The CubeSat program is now proceeding in Japan and U.S. academic institutions and radio groups. CubeSat is a 10cm cubed, 1kg weighted micro-satellite. The first launch of CubeSats is scheduled in May 2002. The second launch will be realized in autumn 2002 or later. Subsequent launch is also planned. Nihon University is going to join the second launch. Our program consists of two phases. At the first phase, we are developing a CubeSat for the second launch opportunity. The purpose of the first phase is that the students learn the whole process of the micro satellite development and operation. At the second phase, we intend to challenge some engineering mission. We have been studying on a mission of deploying an inflatable structure model. In this paper we show the latest status of the first phase of our program , and the plan for the second phase
Charge-Order Pattern of the Low-Temperature Phase of NaV2O5 Uniquely Determined by Resonant X-Ray Scattering from Monoclinic Single Domain
The present resonant x-ray scattering from each of monoclinically-split
single domains of NaV2O5 has critically enhanced contrast between V4+ and V5+
ions strong enough to lead to unambiguous conclusion of the charge-order
pattern of its low-temperature phase below Tc = 35 K. The zig-zag type
charge-order patterns in the -plane previously confirmed have four kinds of
configurations (A, A', B and B') and the stacking sequence along the c-axis is
determined as the AAA'A' type by comparison with model calculations. By
assigning the A and A' configurations to Ising spins, one can reasonably
understand the previously discovered "devil's staircase"-type behavior with
respect to the modulation of the layer-stacking sequences at high pressures and
low temperatures, which very well resembles the global phase diagram
theoretically predicted by the ANNNI model.Comment: 4 pages, 3 figure
A Simple Enzymatic Method for Production of a Wide Variety of D-Amino Acids Using L-Amino Acid Oxidase from Rhodococcus sp. AIU Z-35-1
A simple enzymatic method for production of a wide variety of D-amino acids was developed by kinetic resolution of DL-amino acids using L-amino acid oxidase (L-AAO) with broad substrate specificity from Rhodococcus sp. AIU Z-35-1. The optimum pH of the L-AAO reaction was classified into three groups depending on the L-amino acids as substrate, and their respective activities between pH 5.5 and 8.5 accounted for more than 60% of the optimum activity. The enzyme was stable in the range from pH 6.0 to 8.0, and approximately 80% of the enzyme activity remained after incubation at 40°C for 60 min at pH 7.0. D-Amino acids such as D-citrulline, D-glutamine, D-homoserine or D-arginine, which are not produced by D-aminoacylases or D-hydantoinases, were produced from the racemic mixture within a 24-hr reaction at 30°C and pH 7.0. Thus, the present method using L-AAO was versatile for production of a wide variety of D-amino acids
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
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