32,096 research outputs found
An Imaging and Spectral Study of Ten X-Ray Filaments around the Galactic Center
We report the detection of 10 new X-ray filaments using the data from the
{\sl Chandra} X-ray satellite for the inner ( parsec)
around the Galactic center (GC). All these X-ray filaments are characterized by
non-thermal energy spectra, and most of them have point-like features at their
heads that point inward. Fitted with the simple absorbed power-law model, the
measured X-ray flux from an individual filament in the 2-10 keV band is to ergs cm s and the
absorption-corrected X-ray luminosity is ergs s
at a presumed distance of 8 kpc to the GC. We speculate the origin(s) of these
filaments by morphologies and by comparing their X-ray images with the
corresponding radio and infrared images. On the basis of combined information
available, we suspect that these X-ray filaments might be pulsar wind nebulae
(PWNe) associated with pulsars of age yr. The fact
that most of the filament tails point outward may further suggest a high
velocity wind blowing away form the GC.Comment: 29 pages with 7 figures and 3 pages included. Accepted to Ap
Photoelectric emission from the alkali metal doped vacuum-ice interface
The photoelectron photoemission spectra and thresholds for low coverages of Li and K adsorbed on water-ice have been measured, compared with photoionization spectra of the gas-phase atoms, and modeled by quantum chemical calculations. For both alkali metals the threshold for photoemission is dramatically decreased and the cross section increased on adsorption to the water-ice surface. Quantum chemical calculations suggest that the initial state is formed by the metal atoms adsorbed into the water-ice surface, forming a state with a delocalized electron distribution. This state is metastable and decays on the hundreds of seconds time scale at 92 K. The decay is markedly faster for Li than for K, probably due to diffusion into the ice film
Three-dimensional parton distribution functions and in the polarized proton-antiproton Drell-Yan process
We present predictions of the unweighted and weighted double spin asymmetries
related to the transversal helicity distribution and the longitudinal
transversity distribution , two of eight leading-twist transverse
momentum dependent parton distributions (TMDs) or three-dimensional parton
distribution functions (3dPDFs), in the polarized proton-antiproton Drell-Yan
process at typical kinematics on the Facility for Antiproton and Ion Research
(FAIR). We conclude that FAIR is ideal to access the new 3dPDFs towards a
detailed picture of the nucleon structure.Comment: 6 latex pages, 5 figures, version for publication in EPJ
Time variable cosmological constant of holographic origin with interaction in Brans-Dicke theory
Time variable cosmological constant (TVCC) of holographic origin with
interaction in Brans-Dicke theory is discussed in this paper. We investigate
some characters for this model, and show the evolutions of deceleration
parameter and equation of state (EOS) for dark energy. It is shown that in this
scenario an accelerating universe can be obtained and the evolution of EOS for
dark energy can cross over the boundary of phantom divide. In addition, a
geometrical diagnostic method, jerk parameter is applied to this model to
distinguish it with cosmological constant.Comment: 10 pages, 9 figure
Observation of indirect ionization of W7+ in an electron-beam ion-trap plasma
In this work, visible and extreme ultraviolet spectra of W7+ are measured
using the high-temperature superconducting electron-beam ion trap (EBIT) at the
Shanghai EBIT Laboratory under extremely low-energy conditions (lower than the
nominal electron-beam energy of 130 eV). The relevant atomic structure is
calculated using the flexible atomic code package based on the relativistic
configuration interaction method. The GRASP2K code, in the framework of the
multiconfiguration Dirac-Hartree-Fock method, is employed as well for
calculating the wavelength of the M1 transition in the ground configuration of
W7+. A line from the W7+ ions is observed at a little higher electron-beam
energy than the ionization potential for W4+, making this line appear to be
from W5+. A hypothesis for the charge-state evolution of W7+ is proposed based
on our experimental and theoretical results; that is, the occurrence of W7+
ions results from indirect ionization caused by stepwise excitation between
some metastable states of lower-charge-state W ions, at the nominal
electron-beam energy of 59 eV
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