118630729
The luminosity function of Swift long gamma-ray bursts
The formation rate of long gamma-ray bursts (GRBs) could follow the cosmic star formation rate (SFR) incorporating with cosmic metallicity evolution. Therefore, the luminosity function (LF) of GRBs can in principle be explored by modeling the redshift-luminosity distributions of Swift observed GRBs. For an assumed LF form as �z(L) / e −L p/L (L=Lp) −� (1 + z) � , we found that (1) the approximate broken-power law distribution of the luminosities of the Swift observed GRBs is probably caused by the luminosity selection of the telescope by reducing the number of the GRBs with low luminosities, (2) the evolution of the LF could approach to be very weak, i.e., � � 0, if the GRB environments are metal-poor as Z < (0:1 0:3)Z� , and (3) the slope of the LF can be derived to be within � � (1:55 1:72) by fitting the redshift distribution of the GRBs and qualitatively explaining the luminosity distribution. Finally, we also suggest an empirical detection efficiency as a function of flux for the Swift Burst Alert Telescope (BAT) in order to model the logN logP distribution of the GRBs.
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.
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.
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.
119367954
Further study on 5q configuration states in the chiral SU(3) quark model
The structure of the 5q configuration states with strangeness S = +1 is further studied in the chiral SU(3) quark model based on our previous work. We calculate the energies of fifteen low configurations of the 5q system, four lowest configurations of J(pi) = (1)/(-)(2) with 4q partition [4]orb (0s(4)) [3 1]of, four of J(pi) (1)/(+)(2) with 4q partition [31]orb (0s(3)0p)[4](sigma f) and seven of J(pi) = (1)/(+)(2) with 4q partition [4](orb) (0s(3)0p)[31](sigma f). Some modifications are made in this further study, i.e., the orbital wave function is extended as an expansion of 4 different size harmonic oscillator forms; three various forms (quadratic, linear and error function form) of the color confinement potential are considered; the states with 4q partition [4](orb)(0s(3)0p) [31](sigma f) are added, which are unnegligible in the J(pi) = (1)/(+)(2) case and were not considered in our previous paper, further the mixing between configurations [31](orb)(0s(3)0p)[4](sigma f) and [4]orb (0s(3)0p)[31](sigma f) is also investigated. The results show that the T = 0 state is still always the lowest one for both J(pi) = (1)/(-)(2) and J(pi) = (1)/(+)(2) states, and J(pi) = (1)/(-)(2), T = 0 state is always lower than that of J(pi) = (1)/(+)(2), All of these modifications can only offer several tens to hundred MeV effect, and the theoretical value of the lowest state is still about 245 MeV higher than the experimental mass of theta(+). It seems to be difficult to get the calculated mass close to the observed one with the reasonable parameters in the framework of the chiral SU(3) quark model when the model space is chosen as a 5q cluster. (c) 2005 Elsevier B.V. All rights reserved.
122517767
Structure of H-dihyperon
The structure of H dihyperon (DH) is investigated by employing the SU (3) chiral quark model. As the structure of DH, two different configurations, six-quark cluster configuration and two-cluster configuration, are considered respectively. The result shows that except the sigma chiral field, the overall effect of the other SU (3) chiral fields is destructive in forming a stable DH and the two-cluster configuration is the preferred structure. The resultant mass of DH in a three-coupled-channel calculation in the SU (3) chiral quark model is ranged from 2225 to 2234 MeV.
124840990
Equivalent local N Y potentials with S = -1 in quark cluster model
181353095
Color screening effect in b anti-b system
115307247
E2/M1 ratio of the Delta gamma N transition within the chiral constituent quark model