118964566
DETERMINING THE LUMINOSITY FUNCTION OF SWIFT LONG GAMMA-RAY BURSTS WITH PSEUDO-REDSHIFTS
The determination of the luminosity function (LF) of gamma-ray bursts (GRBs) is an important role for the cosmological applications of the GRBs, which, however, is seriously hindered by some selection effects due to redshift measurements. In order to avoid these selection effects, we suggest calculating pseudo-redshifts for Swift GRBs according to the empirical L-Ep relationship. Here, such a L-Ep relationship is determined by reconciling the distributions of pseudo- and real redshifts of redshift-known GRBs. The values of Ep taken from Butler's GRB catalog are estimated with Bayesian statistics rather than observed. Using the GRB sample with pseudo-redshifts of a relatively large number, we fit the redshift-resolved luminosity distributions of the GRBs with a broken-power-law LF. The fitting results suggest that the LF could evolve with redshift by a redshift-dependent break luminosity, e.g., Lb = 1.2 × 1051(1 + z)2 erg s–1. The low- and high-luminosity indices are constrained to 0.8 and 2.0, respectively. It is found that the proportional coefficient between the GRB event rate and the star formation rate should correspondingly decrease with increasing redshifts.
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.
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
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.
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.
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.
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.
125842933
Omega omega states in a chiral quark model
The structures of Omega omega states with spin-parity J(P) = 5/2(-), 3/2(-), and 1/2(-) are dynamically studied in both the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving a resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the energies of the baryon ground states, the binding energy of the deuteron, the nucleon-nucleon (NN) scattering phase shifts, and the hyperon-nucleon (YN) cross sections. The calculated results show that the Omega omega state has an attractive interaction, and in the extended chiral SU(3) quark model such attraction can make for a Omega omega quasi-bound state with spin-parity JP = 3/2- or 5/2- and the binding energy of about several MeV.
15263185
Baryon-Meson Interactions in Chiral Quark Model
Using the resonating group method (RGM), we dynamically study the baryon-meson interactions in chiral quark model. Some interesting results are obtained: (1) The Sigma K state has an attractive interaction, which consequently results in a Sigma K quasibound state. When the channel coupling of Sigma K and Lambda K is considered, a sharp resonance appears between the thresholds of these two channels. (2) The interaction of Delta K state with isospin I=1 is attractive, which can make for a Delta K quasibound state. (3) When the coupling to the Lambda K* channel is considered, the N phi is found to be a quasibound state in the extended chiral SU(3) quark model with several MeV binding energy. (4) The calculated S-, P-, D-, and F-wave KN phase shifts achieve a considerable improvement in not only the signs but also the magnitudes in comparison with other's previous quark model study.
15517927
Resonating group method study of kaon-nucleon elastic scattering in the chiral SU(3) quark model
The chiral SU(3) quark model is extended to include an antiquark in order to study the kaon-nucleon system. The model input parameters b{sub u}, m{sub u}, m{sub s} are taken to be the same as in our previous work which focused on the nucleon-nucleon and nucleon-hyperon interactions. The mass of the scalar meson {sigma} is chosen to be 675 MeV and the mixing of {sigma}{sub 0} and {sigma}{sub 8} is considered. Using this model the kaon-nucleon S and P partial waves phase shifts of isospin I=0 and I=1 have been studied by solving a resonating group method equation. The numerical results of S{sub 01}, S{sub 11}, P{sub 01}, P{sub 03}, and P{sub 11} partial waves are in good agreement with the experimental data while the phase shifts of P{sub 13} partial wave are a little bit too repulsive when the laboratory momentum of the kaon meson is greater than 500 MeV in this present calculation.
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.