67 research outputs found
A different view of wind in X-ray binaries: the accretion disc corona source 2S 0921-630
Accretion disc coronae (ADC) sources are very high inclination neutron star or black hole binaries, where the outer accretion flow blocks a direct view of the central source. The weak observed X-ray emission is instead produced mainly by scattering of the intrinsic radiation from highly ionized gas surrounding the source, the ADC. However, the origin of this scattering material is still under debate. We use the ADC source 2S 0921-630 (V395 Car) to test whether it is consistent with a thermal-radiative wind produced by the central X-ray source illuminating and puffing up the outer disc. This wind is clearly visible in blueshifted absorption lines in less highly inclined systems, where the source is seen directly through this material. Using the phenomenological photoionized plasma model, we first characterize the parameter that drives emission lines observed in 2S0921 in XMM–Newton and Chandra data. Following this, we run the Monte Carlo radiation transfer simulation to get scattered/reprocessed emissions in the wind, with the density and velocity structure obtained from the previous work. Our model agrees with all the wind emission lines in the Chandra high and medium energy grating spectra for an intrinsic source luminosity of L > 0.2 LEdd. This result strongly favours thermal-radiative winds as the origin of the ADC. We also show how high-resolution spectra via microcalorimeters can provide a definitive test by detecting blueshifted absorption lines
Prospect for Future MeV Gamma-ray Active Galactic Nuclei Population Studies
While the X-ray, GeV gamma-ray, and TeV gamma-ray skies have been extensively
studied, the MeV gamma-ray sky is not well investigated after the Imaging
Compton Telescope (COMPTEL) scanned the sky about two decades ago. In this
paper, we investigate prospects for active galactic nuclei population studies
with future MeV gamma-ray missions using recent spectral models and luminosity
functions of Seyfert and flat spectrum radio quasars (FSRQs). Both of them are
plausible candidates as the origins of the cosmic MeV gamma-ray background. If
the cosmic MeV gamma-ray background radiation is dominated by non-thermal
emission from Seyferts, the sensitivity of 10^-12 erg cm^-2 s^-1 is required to
detect several hundred Seyferts in the entire sky. If FSRQs make up the cosmic
MeV gamma-ray background, the sensitivity of ~4 x 10^-12 erg cm^-2 s^-1 is
required to detect several hundred FSRQs following the recent FSRQ X-ray
luminosity function. However, based on the latest FSRQ gamma-ray luminosity
function, with which FSRQs can explain up to ~30% of the MeV background, we can
expect several hundred FSRQs even with the sensitivity of 10^-11 erg cm^-2 s^-1
which is almost the same as the sensitivity goal of the next generation MeV
telescopes.Comment: 9 pages, 5 figures, accepted for publication in PAS
Fabrication of submicron alumina ceramics by pulse electric current sintering using M(2+) (M = Mg, Ca, Ni)-doped alumina nanopowders
Dense submicron-grained alumina ceramics were fabricated by pulse electric current sintering (PECS) using M(2+)(M: Mg, Ca, Ni)-doped alumina nanopowders at 1250 degrees C under a uniaxial pressure of 80 MPa. The M(2+)-doped alumina nanopowders (0-0.10 mass%) were prepared through a new sol-gel route using high-purity polyhydroxoaluminum (PHA) and MCl(2) solutions as starting materials. The composite gels obtained were calcined at 900 degrees C and ground by planetary ball milling. The powders were re-calcined at 900 degrees C to increase the content of a-alumina particles, which act as seeding for low-temperature densification. Densification and microstructural development depend on the M(2+) dopant species. Dense alumina ceramics (relative density >= 99.0%) thus obtained had a uniform microstructure composed of fine grains, where the average grain size developed for non-doped, Ni-doped, Mg-doped and Ca-doped samples was 0.67, 0.67, 0.47 and 0.30 mu m, respectively, showing that Ca-doping is the most promising method for tailoring of nanocrystalline alumina ceramics. (c) 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved.ArticleCERAMICS INTERNATIONAL. 35(5):1845-1850 (2009)journal articl
Densification of rare-earth (Lu, Gd, Nd)-doped alumina nanopowders obtained by a sol-gel route under seeding
Rare-earth (RE: Lu, Gd, Nd, 0.10 mol%)-doped alumina nanopowders were prepared by a new sol-gel route using polyhydroxoaluminum (PHA) and RECl(3) Solutions under alpha-alumina (similar to 75 nm) seeding. Among the rare-earth dopants studied, Lu yields the most suitable nanopowders for low-temperature densification. The 0.10 mol% Lu-doped nanopowders, which were obtained at a calcination temperature of 900 degrees C under 5 mass % alpha-alumina seeding, consisted of similar to 80-nm alpha-alumina particles and gamma-alumina nanoparticles. Using these Lu-doped alumina nanopowders, fully densified alumina ceramics with a uniform microstructure composed of fine grains with an average size of 0.61 mu m could be obtained at 1400 degrees C by pressureless sintering. Clearly, the Lu-doped nanopowders obtained here represent a viable option for fabricating dense, finer-grained alumina ceramics because an undoped sample with 5 mass% seeds gave a microstructure with an average grain size of 1.78 mu m at 1400 degrees C. (C) 2009 Elsevier B.V. All rights reserved.ArticlePOWDER TECHNOLOGY. 193(1):26-31 (2009)journal articl
Orbital- and spin-phase variability in the X-ray emission from the accreting pulsar Cen X-3
We analyzed 39 ks NuSTAR observation data of the high mass X-ray binary Cen
X-3 in order to investigate the orbital- and spin-phase spectral variability.
The observation covers the orbital phase of - of the source,
where corresponds to the mid-eclipse. The orbital-phase-resolved
spectroscopy revealed that low energy photons are more dominant for the
spectral fluctuation, and a large part of the variability can be explained in
terms of absorption by clumps of stellar wind. The spin-phase-resolved
spectroscopy together with energy-resolved pulse profiles, on the other hand,
presented large flux variations in high energy bands, which suggests that the
origin of the variability is the different efficiency of Comptonization inside
the accretion column. The energy band which includes Fe emission lines or
cyclotron resonance scattering feature (CRSF) shows distinct variability
compared to the nearby bands. The Fe lines show low variability along the spin
phase, which indicates that the emission regions are apart from the neutron
star. The central energy and strength of the CRSF are both positively
correlated with the spin-phase-resolved flux, which suggests that the emitted
photons face stronger magnetic fields and deeper absorption when they come from
high-flux regions. We also examined the independence of the orbital- and
spin-phase variability. They showed no correlation with each other and were
highly independent, which implies the accretion stream is stable during the
observation.Comment: 20 pages, 12 figures, accepted for publication in Ap
Circumnuclear Multi-phase Gas in the Circinus Galaxy. V. The Origin of the X-Ray Polarization in the Circinus Galaxy
The Imaging X-ray Polarimetry Explorer (IXPE) detected X-ray polarization in
the nearest Seyfert 2 galaxy, the Circinus galaxy, for the first time. To
reproduce the IXPE results, we computed the degree of polarization based on two
types of radiative hydrodynamic simulations: a parsec-scale three-dimensional
model and a sub-parsec-scale axisymmetric model with a higher spatial
resolution. In a series of papers, we confirmed that these models naturally
explain the multi-wavelength observations of the Circinus galaxy from radio to
X-rays. We used a Monte Carlo Simulation for Astrophysics and Cosmology code to
compute the linear polarization of continuum emission. We found that the degree
of polarization based on the parsec-scale radiation-driven fountain model was
smaller than that observed with the IXPE. The degree of polarization based on
the sub-parsec-scale model depends on the hydrogen number density of the disk
(), and the degree of polarization obtained from our simulation is
consistent with that observed with the IXPE in the case of . We investigate where the photons are Compton
scattered and imply that the origin of the X-ray polarization in the Circinus
galaxy is the outflow inside . In this case, the degree of
polarization may change over a timescale of approximately ten years.Comment: 11 pages, 8 figures, accepted for publication in Ap
Application of X-Ray Clumpy Torus Model (XCLUMPY) to 10 Obscured Active Galactic Nuclei Observed with Suzaku and NuSTAR
We apply XCLUMPY, an X-ray spectral model from a clumpy torus in an active
galactic nucleus (AGN), to the broadband X-ray spectra of 10 obscured AGNs
observed with both Suzaku and NuSTAR. The infrared spectra of these AGNs were
analyzed with the CLUMPY code. Since XCLUMPY adopts the same clump distribution
as that in the CLUMPY, we can directly compare the torus parameters obtained
from the X-ray spectra and those from the infrared ones. The torus angular
widths determined from the infrared spectra () are
systematically larger than those from the X-ray data ();
the difference () correlates with the
inclination angle determined from the X-ray spectrum. These results can be
explained by the contribution from dusty polar outflows to the observed
infrared flux, which becomes more significant at higher inclinations (more
edge-on views). The ratio of the hydrogen column density and V-band extinction
in the line of sight absorber shows large scatter (1 dex) around the
Galactic value, suggesting that a significant fraction of AGNs have dust-rich
circumnuclear environments.Comment: 17 pages, 3 figures, accepted for publication in Ap
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