1,881 research outputs found
Extended RPA with ground-state correlations in a solvable model
The ground states and excited states of the Lipkin model hamiltonian are
calculated using a new theoretical approach which has been derived from an
extended time-dependent Hartree-Fock theory known as the time-dependent
density-matrix theory (TDDM). TDDM enables us to calculate correlated ground
states, and its small amplitude limit (STDDM), which is a version of extended
RPA theories based on a correlated ground state, can be used to calculate
excited states. It is found that this TDDM plus STDDM approach gives much
better results for both the ground states and the excited states than the
Hartree-Fock ground state plus RPA approach.Comment: 4 pages, 4 figure
Modulation Mechanism of TeV, GeV, and X-ray Emission in LS5039
The emission mechanism of the gamma-ray binary LS5039 in energy bands of TeV,
GeV, and X-ray is investigated. Observed light curves in LS5039 show that TeV
and GeV fluxes anticorrelate and TeV and X-ray fluxes correlate. However, such
correlated variations have not been explained yet reasonably at this stage.
Assuming that relativistic electrons are injected constantly at the location of
the compact object as a point source, and that they lose energy only by the
inverse Compton (IC) process, we calculate gamma-ray spectra and light curves
by the Monte Carlo method, including the full electromagnetic cascade process.
Moreover, we calculated X-ray spectra and light curves by using the resultant
electron distribution. As a result, we are able to reproduce qualitatively
spectra and light curves observed by HESS, Fermi, and Suzaku for the
inclination angle i = 30 dig and the index of injected electron distribution p
= 2.5. We conclude that TeV-GeV anticorrelation is due to anisotropic IC
scattering and anisotropic gamma-gamma absorption, and that TeV-X correlation
is due to the dependence of IC cooling time on orbital phases. In addition, the
constraint on the inclination angle implies that the compact object in LS5039
is a black hole.Comment: 27 pages, 7 figures, published in The Astrophysical Journa
The Variation of Gas Mass Distribution in Galaxy Clusters: Effects of Preheating and Shocks
We investigate the origin of the variation of the gas mass fraction in the
core of galaxy clusters, which was indicated by our work on the X-ray
fundamental plane. The adopted model supposes that the gas distribution
characterized by the slope parameter is related to the preheated temperature.
Comparison with observations of relatively hot (~> 3 keV) and low redshift
clusters suggests that the preheated temperature is about 0.5-2 keV, which is
higher than expected from the conventional galactic wind model and possibly
suggests the need for additional heating such as quasars or gravitational
heating on the largest scales at high redshift. The dispersion of the preheated
temperature may be attributed to the gravitational heating in subclusters. We
calculate the central gas fraction of a cluster from the gas distribution,
assuming that the global gas mass fraction is constant within a virial radius
at the time of the cluster collapse. We find that the central gas density thus
calculated is in good agreement with the observed one, which suggests that the
variation of gas mass fraction in cluster cores appears to be explained by
breaking the self-similarity in clusters due to preheated gas. We also find
that this model does not change major conclusions on the fundamental plane and
its cosmological implications obtained in previous papers, which strongly
suggests that not only for the dark halo but also for the intracluster gas the
core structure preserves information about the cluster formation.Comment: 17 pages, to be published in Ap
Nuclear prolate-shape dominance with the Woods-Saxon potential
We study the prolate-shape predominance of the nuclear ground-state
deformation by calculating the masses of more than two thousand even-even
nuclei using the Strutinsky method, modified by Kruppa, and improved by us. The
influences of the surface thickness of the single-particle potentials, the
strength of the spin-orbit potential, and the pairing correlations are
investigated by varying the parameters of the Woods-Saxon potential and the
pairing interaction. The strong interference between the effects of the surface
thickness and the spin-orbit potential is confirmed to persist for six sets of
the Woods-Saxon potential parameters. The observed behavior of the ratios of
prolate, oblate, and spherical nuclei versus potential parameters are rather
different in different mass regions. It is also found that the ratio of
spherical nuclei increases for weakly bound unstable nuclei. Differences of the
results from the calculations with the Nilsson potential are described in
detail.Comment: 16 pages, 17 figure
The X-ray Jet in Centaurus A: Clues on the Jet Structure and Particle Acceleration
We report detailed studies of the X-ray emission from the kpc scale jet in
the nearest active galaxy, Cen A. 41 compact sources were found within the jet,
13 of which were newly identified. We construct the luminosity function for the
detected jet-knots and argue that the remaining emission is most likely to be
truly diffuse, rather than resulting from the pile-up of unresolved faint
knots. The transverse jet profile reveals that the extended emission has the
intensity peak at the jet boundaries. We note that limb-brightened jet
morphologies have been observed previously at radio frequencies in some jet
sources, but never so clearly at higher photon energies. Our result therefore
supports a stratified jet model, consisting of a relativistic outflow including
a boundary layer with a velocity shear. In addition, we found that the X-ray
spectrum of the diffuse component is almost uniform across and along the jet.
We discuss this spectral behavior within a framework of shock and stochastic
particle acceleration processes. We note some evidence for a possible spectral
hardening at the outer sheath of the jet. Due to the limited photon statistics
of the present data, further deep observations of Cen A are required to
determine the reality of this finding, however we note that the existence of
the hard X-ray features at outer jet boundaries would provide an important
challenge to theories for the evolution of ultra-relativistic particles within
the jets.Comment: 27page, 8 figures, ver2, accepted for publication in the Ap
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