119273299
The Newly Born Magnetars Powering Gamma-Ray Burst Internal-Plateau Emission: Are There Strange Stars?
The internal-plateau X-ray emission of gamma-ray bursts (GRBs) indicates that a newly born magnetar could be the central object of some GRBs. The observed luminosity and duration of the plateaus suggest that, for such a magnetar, a rapid spin with a sub- or millisecond period is sometimes able to last thousands of seconds. In this case, the conventional neutron star (NS) model for the magnetar may be challenged, since the rapid spin of nascent NSs would be remarkably decelerated within hundreds of seconds due to r-mode instability. In contrast, the r-modes can be effectively suppressed in nascent strange stars (SSs). In other words, to a certain extent, only SSs can keep nearly constant extremely rapid spin for a long period of time during the early ages of the stars. We thus propose that the sample of the GRB rapidly spinning magnetars can be used to test the SS hypothesis based on the distinct spin limits of NSs and SSs.
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
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.
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.
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.
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.
120930803
SPIN-ORBIT FORCE OF HYPERON-NUCLEON INTERACTION IN THE CHIRAL SU(3) QUARK MODEL
The spin-orbit (LS) force of the hyperon-nucleon interaction is studied in the chiral SU(3) quark model. The symmetric LS terms from the one gluon exchange (OGE) and the scalar nonet exchange (OSE) are taken into account. It is shown that two different treatments (the LS coupling from either OGE or OSE being artificially enhanced in order to reproduce the P-3(J) phase shifts of the nucleon-nucleon scattering) lead to very similar LS couplings in the Sigma N(I = 3/2) channel but give quite different results in the Lambda N - Sigma N(I = 1/2) coupled-channel system. A prominent resonance occurs in the P-1(1) state of the Lambda N channel mainly due to the stronger LS(-) couplings in the Lambda N - Sigma N(I = 1/2) coupled-channel system in the OGE enhanced case. Comparatively the Lambda N P-1(1) phase shift curve exhibits a rather smooth behaviour in the OSE enhanced case. Comparing our theoretical results with the experimental data available, and considering the requirement of the baryon spectrum, one can deduce that a stronger color-independent LS coupling is preferred in the chiral quark model. (C) 1998 Elsevier Science B.V.
13963563
Dibaryon systems in chiral SU(3) quark model
The possible candidates of S-wave dibaryons with various strange numbers are studied under the chiral SU(3) quark model. It is shown that there are three types of baryon-baryon bound states. The states of the first type are called deuteron-like states. If chiral fields can provide enough attraction between interacting baryons, these systems, such as [Xi Omega - Xi*Omega]((1,1/2)), [Xi Xi]((0,1)), [N Omega]((2,1/2)) would be weakly bound. The states of the second type such as [Sigma*Delta]((0,5/2)), [Sigma*Delta]((3,1/2)), [Delta Delta](0,3) and [Delta Delta]((3,0)) are named as Delta Delta -like states. Due to the highly symmetric character in orbital space, these systems could be relatively deeply bound, but the strong decay modes of composed baryons cause the widths of the states much broader. The states of the third type are entitled as Omega Omega -like states. Due to the same symmetry character shown in the systems of the second type and the only weak decay mode of composed baryons, for instance in [Omega Omega](0,0), or at most one strong decay mode of composed baryons, for example in [Xi*Omega]((0,1/2)), these states are deeply bound states with narrow widths. The states of latter two types are most interesting new dibaryon states and should be carefully investigated both theoretically and experimentally. (C) 2001 Elsevier Science B,V. All rights reserved.
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.
118201784
A New Dibaryon System (OmegaOmega)0+ in Chiral SU(3) Quark Model
119898677
Baryon spectrum in quark potential model
In the calculation of the baryonic spectrum in the quark potential model, except the conventional one-gluon-exchange term (OGE) in the quark-quark interaction, de­ rived by Rujula, Georgi and Glashow[l] , a confinement potential should be introduced into the hamiltonian of the baryon. Although a linear type confinement potential is expected by the lattice gauge theory and string model, the exact form of this potential is still unknown. Thus, in the practical calculation, tltis potential should phenomeno­ logically be introduced. In order to explain the experimental phenomenon why in the baryonic spectrum, the excited states with positive parity are very close to the ',' states with negative parity in the baryonic spectrum, the confinement potentiaisill various forms are employed in the calculation. By selecting ~ confinement p'otential in the form of the combination of the linear and quadratic terms, C. S. Kalman and Traln[2) obtained a better agreement between the theoretical resnlt and experinlental data.