15555566
X-RAY AND HIGH-ENERGY FLARES FROM LATE INTERNAL SHOCKS OF GAMMA-RAY BURSTS
We study afterglow flares of gamma-ray bursts (GRBs) in the framework of the late internal shock (LIS) model based on a careful description for the dynamics of a pair of shocks generated by a collision between two homogeneous shells. First, by confronting the model with some fundamental observational features of X-ray flares, we find some constraints on the properties of the pre-collision shells that are directly determined by the central engine of GRBs. Second, high-energy emission associated with X-ray flares, which arises from synchrotron self-Compton emission of LISs, is investigated in a wide parameter space. The predicted flux of high-energy flares may reach as high as ~10–8 erg cm–2 s–1, which is likely to be detectable with the Large Area Telescope aboard the Fermi Space Telescope (formerly GLAST).
119705192
Preliminary study of the K N interaction in a chiral constituent quark model
A preliminary investigation of $\overline{K}N$ interaction is performed within a chiral constituent quark model by solving the resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the $S$-, $P$-, $D$-, $F$-wave $\mathit{KN}$ scattering phase shifts. The channel-coupling between $\overline{K}N,\ensuremath{\pi}\ensuremath{\Lambda}$ and $\ensuremath{\pi}\ensuremath{\Sigma}$ is considered, and the scattering phase shifts as well as the bound-state problem of $\overline{K}N$ are dynamically studied. The results show that the $S$-wave $\overline{K}N$ interaction in the isospin $I=0$ channel is attractive, and in the extended chiral SU(3) quark model such an attraction can make for a $\overline{K}N$ bound state, which appears as a $\ensuremath{\pi}\ensuremath{\Sigma}$ resonance in the coupled-channel calculation, while the chiral SU(3) quark model cannot accommodate the existence of a $\overline{K}N$ bound state. It seems that the vector meson exchanges are necessary to be introduced in the quark-quark interactions if one tries to explain the $\ensuremath{\Lambda}(1405)$ as a $\overline{K}N$ bound state or a $\ensuremath{\pi}\ensuremath{\Sigma}$-$\overline{K}N$ resonance state.
121120033
Yields and isomeric ratio of xenon and krypton isotopes from thermal neutron fission of /sup 235/U
The experimental cumulative yields of /sup 85/Kr/sup m/, /sup 87/Kr, /sup 88/Kr, /sup 133/Xe/sup g/, /sup 135/Xe/sup m/, and /sup 135/Xe/sup g/ and the independent isomeric yield of /sup 133/Xe/sup m/ in the thermal neutron fission of /sup 235/U have been measured by the gas chromatographic method. The independent yields of /sup 133/Xe/sup g/, /sup 135/Xe/sup m/, and /sup 135/Xe/sup g/ were deduced with the aid of /sup 133/I and /sup 135/I data. The isomeric yield ratios of /sup 133/Xe and /sup 135/Xe have been computed and compared with theoretical values since they have the same high spin state J = 11/2/sup -/ and low spin ground state J = 3/2/sup +/. The influence of the shell effect on the fission isomeric yield ratio is discussed. From the measured independent yield of Xe isotopes plus the reported data, the Xe-isotopic distribution curve has been constructed. The curve is compared with the isotopic distribution curves of Xe isotopes formed in 11.5 GeV proton interactions with /sup 238/U and Cs isotopes formed in 24 GeV proton interactions with /sup 238/U. Upon fitting the yield curves we find that only those products with N/Z> or =1.48 fit a curve typical of a binarymore » fission process.« less
52103890
A past capture event at Sagittarius A* inferred from the fluorescent X-ray emission of Sagittarius B clouds
The fluorescent X-ray emission from neutral iron in the molecular clouds [Sagittarius (Sgr) B] indicates that the clouds are being irradiated by an external X-ray source. The source is probably associated with the Galactic central black hole (Sgr A*), which triggered a bright outburst 100 yr ago. We suggest that such an outburst could be due to a partial capture of a star by Sgr A*, during which a jet was generated. Using constraints from the observed flux and the time variability (∼10 yr) of the Sgr B fluorescent emission, we find that the shock produced by the interaction of the jet with the dense interstellar medium represents a plausible candidate for the X-ray source emission.
120879129
Effect of a strong magnetic field on the surface electric field of strange stars
We made a detailed study of the properties of the electron layer near the quark surface of strange stars with strong (${\sim}10^{14}{-}10^{17}$ G) magnetic fields. The electrostatic potential and the electric field at the quark surface were calculated as functions of the magnetic field intensity of bare strange stars. Using an ultrastrong ($B\geq 2.5\times10^{16}$ G) magnetic field, we found that the distribution of electrons becomes an exponential function of radial distance, which is quite different in a magnetic field-free case. We also calculated the variation in gap width between the strange core and the normal nuclear crust for strange stars, which is due to magnetic field effect.
119022638
A statistical classification of the unassociated gamma-ray sources in the second Fermi Large Area Telescope Catalog
With the assistance of the identified/associated sources in the second Fermi Large Area Telescope (LAT) catalog, we analyze and resolve the spatial distribution and the distributions of the gamma-ray spectral and variability indices of the remaining 575 unassociated Fermi LAT sources. Consequently, it is suggested that the unassociated sources could statistically consist of Galactic supernova remnants/pulsar wind nebulae, BL Lacertae objects, flat spectrum radio quasars and other types of active galaxies with fractions of 25%, 29%, 41% and 5%, respectively.
181353095
Color screening effect in b anti-b system
119487137
Coupled-channels study of Lambda K and Sigma K states in the chiral SU(3) quark model
The S-wave $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K$ states with isospin $I=1/2$ are dynamically investigated within the framework of the chiral SU(3) quark model by solving a resonating group method equation. The model parameters are taken from our previous work, which gave a good description of the energies of the baryon ground states, the binding energy of the deuteron, and the experimental data of the nucleon-nucleon (NN) and nucleon-hyperon (NY) scattering. Assumed not to give important contributions in the scattering processes, the s-channel quark-antiquark ($q\overline{q}$) annihilation interactions are not included as a first step. The results show a strong attraction between \ensuremath{\Sigma} and K, which consequently results in a $\ensuremath{\Sigma}K$ quasibound state with about 17-MeV binding energy, unlike the case of $\ensuremath{\Lambda}K$, which is unbound. When the channel coupling of $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K$ is considered, a sharp resonance state near 1670 MeV with spin-parity ${J}^{P}=1/{2}^{\ensuremath{-}}$ is found. The narrow gap of the $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K$ thresholds, the strong attraction between \ensuremath{\Sigma} and K, and the sizable off-diagonal matrix elements of $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K$ are responsible for the appearance of this resonance.
121548156
BARYON–BARYON INTERACTION IN THE EXTENDED CHIRAL SU(3) QUARK MODEL
The hyperon-nucleon scattering processes and some dibaryon states are studied both in the chiral SU(3) quark model and in the extended chiral SU(3) quark model by solving the resonating group method (RGM) equation. We find that the short-range interaction could be described either by the one-gluon exchange or by the vector meson exchange for baryon-baryon system.
115699498
A study of nucleon-nucleon spin-orbit force in quark model
Abstract Spin-orbit interactions between two quarks due to the one-gluon exchange, confinement potential, σ-exchange of the chiral field and two-gluon exchange are considered in our calculation. As a consequence, the spin-orbit energy splitting of the 1P state in the baryon spectrum and the 3 P 2 phase shifts of NN scattering can unifiedly be explained.
120693974
Strange hadronic matter in a chiral SU(3) quark mean-field model
A quark-meson coupling model based on SU(3)(L) x SU(3)(R) symmetry and scale invariance is proposed, We apply this chiral SU(3) quark mean-field model to investigate strange hadronic matter including Lambda, Sigma and Xi hyperons, With the symmetry-breaking term, all the hyperon potentials are reasonable. The effective baryon masses, binding energy and hyperon ratios are discussed with four types of confining potentials. (C) 2001 Elsevier Science B.V. All rights reserved.