6,615 research outputs found
Spectral Analyses of the Nearest Persistent Ultraluminous X-Ray Source M33 X-8
We provide a detailed analysis of 12 XMM observations of the nearest
persistent extragalactic ultraluminous X-ray source (ULX), M33 X-8. No
significant spectral evolution is detected between the observations, therefore
we combine the individual observations to increase the signal-to-noise ratio
for spectral fitting. The combined spectra are best fitted by the
self-consistent p-free disk plus power-law component model with p =
0.571_{-0.030}^{+0.032}, kT_{in} = 1.38_{-0.08}^{+0.09} keV, and the flux ratio
of the p-free disk component to the power-law component being 0.63:0.37 in the
0.3 -- 10 keV band. The fitting indicates that the black hole in M33 X-8 is of
\sim 10 M_{\odot} and accretes at a super-Eddington rate (\sim 1.5 L_{Edd}),
and the phase of the accretion disk is close to a slim disk (p = 0.5). We
report, for the first time, that an extra power-law component is required in
addition to the p-free disk model for ULXs. In super-Eddington cases, the
power-law component may possibly result from the optically thin inner region f
the disk or a comptonized corona similar to that of a standard thin disk.Comment: 11 pages, 1 table, 2 figures, accepted by PAS
Effects of dust storms on microwave radiation based on satellite observation and model simulation over the Taklamakan desert
International audienceEffects of dust particles on microwave radiation over the Taklamakan desert are studied with use of measurements from the Advanced Microwave Scanning Radiometer (AMSR-E) on the EOS Aqua satellite and a microwave radiation transfer model. Eight observed cases show that the signal from atmospheric dust can be separated from the surface radiation by the fact that the dust particles produce stronger scattering at high frequencies and depolarize the background desert signature. This result of satellite data is consistent with the model simulation
Mott physics, sign structure, ground state wavefunction, and high-Tc superconductivity
In this article I give a pedagogical illustration of why the essential
problem of high-Tc superconductivity in the cuprates is about how an
antiferromagnetically ordered state can be turned into a short-range state by
doping. I will start with half-filling where the antiferromagnetic ground state
is accurately described by the Liang-Doucot-Anderson (LDA) wavefunction. Here
the effect of the Fermi statistics becomes completely irrelevant due to the no
double occupancy constraint. Upon doping, the statistical signs reemerge,
albeit much reduced as compared to the original Fermi statistical signs. By
precisely incorporating this altered statistical sign structure at finite
doping, the LDA ground state can be recast into a short-range antiferromagnetic
state. Superconducting phase coherence arises after the spin correlations
become short-ranged, and the superconducting phase transition is controlled by
spin excitations. I will stress that the pseudogap phenomenon naturally emerges
as a crossover between the antiferromagnetic and superconducting phases. As a
characteristic of non Fermi liquid, the mutual statistical interaction between
the spin and charge degrees of freedom will reach a maximum in a
high-temperature "strange metal phase" of the doped Mott insulator.Comment: 12 pages, 12 figure
Spin-charge separation in the single hole doped Mott antiferromagnet
The motion of a single hole in a Mott antiferromagnet is investigated based
on the t-J model. An exact expression of the energy spectrum is obtained, in
which the irreparable phase string effect [Phys. Rev. Lett. 77, 5102 (1996)] is
explicitly present. By identifying the phase string effect with spin backflow,
we point out that spin-charge separation must exist in such a system: the doped
hole has to decay into a neutral spinon and a spinless holon, together with the
phase string. We show that while the spinon remains coherent, the holon motion
is deterred by the phase string, resulting in its localization in space. We
calculate the electron spectral function which explains the line shape of the
spectral function as well as the ``quasiparticle'' spectrum observed in
angle-resolved photoemission experiments. Other analytic and numerical
approaches are discussed based on the present framework.Comment: 16 pages, 9 figures; references updated; to appear in Phys. Rev.
Magnetic Incommensurability in Doped Mott Insulator
In this paper we explore the incommensurate spatial modulation of spin-spin
correlations as the intrinsic property of the doped Mott insulator, described
by the model. We show that such an incommensurability is a direct
manifestation of the phase string effect introduced by doped holes in both one-
and two-dimensional cases. The magnetic incommensurate peaks of dynamic spin
susceptibility in momentum space are in agreement with the neutron-scattering
measurement of cuprate superconductors in both position and doping dependence.
In particular, this incommensurate structure can naturally reconcile the
neutron-scattering and NMR experiments of cuprates.Comment: 12 pages (RevTex), five postscript figure
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