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.
41248825
Yield and recoil properties of iodine isotopes from the interaction of 240 MeV 12C with 238U.
The independent yields, recoil properties, and forward-to-backward ratios (F/B) of iodine isotopes from the interaction of 240 MeV /sup 12/C with /sup 238/U have been measured radiochemically by the thick-target/thick-catcher method. The isotopic yield distribution curve has been constructed and is found to consist of two overlapping Gaussians, peaking at A = 126.5 and 133.8 with width parameters of 2.29 and 2.04 mass units, respectively. All the measured iodine isotopes had ranges of 7.7 +- 0.4 mg/cm/sup 2/. The neutron-deficient products have F/B of 1.76 +- 0.14, but the neutron-excessive products have F/B of only 1.09 +- 0.06. The yield curve was analyzed with the liquid drop model and the recoil curve was analyzed by the standard two-step vector model; the results show that the neutron-deficient products are formed from nonequilibrium processes and the neutron-excessive products are formed from the normal low-energy fission process.
15648290
Long-term evolution and gravitational wave radiation of neutron stars with differential rotation induced by r-modes
In a second-order r-mode theory, Sa and Tome found that the r-mode oscillation in neutron stars (NSs) could induce stellar differential rotation, which naturally leads to a saturated state of the oscillation. Based on a consideration of the coupling of the r-modes and the stellar spin and thermal evolution, we carefully investigate the influences of the differential rotation on the long-term evolution of isolated NSs and NSs in low-mass X-ray binaries, where the viscous damping of the r-modes and its resultant effects are taken into account. The numerical results show that, for both kinds of NSs, the differential rotation can significantly prolong the duration of the r-modes. As a result, the stars can keep nearly a constant temperature and constant angular velocity for over a thousand years. Moreover, the persistent radiation of a quasi-monochromatic gravitational wave would also be predicted due to the long-term steady r-mode oscillation and stellar rotation. This increases the detectability of gravitational waves from both young isolated and old accreting NSs.
119289155
HIGH-ENERGY GAMMA-RAY AFTERGLOWS FROM LOW-LUMINOSITY GAMMA-RAY BURSTS
The observations of gamma-ray bursts (GRBs) such as 980425, 031203 and 060218, with luminosities much lower than those of other classic bursts, lead to the definition of a new class of GRBs—LL-GRBs. The nature of the outflow responsible for them is not yet clear. Two scenarios have been suggested: one is the conventional relativistic outflow with initial Lorentz factor of order of Γ0 10 and the other is a trans-relativistic outflow with Γ0 1-2. Here, we compare the high-energy gamma-ray afterglow emission from these two different models, taking into account both synchrotron self-inverse Compton (SSC) scattering and the external inverse Compton scattering due to photons from the cooling supernova or hypernova envelope (SNIC). We find that the conventional relativistic outflow model predicts a relatively high gamma-ray flux from SSC at early times (<104 s for typical parameters) with a rapidly decaying light curve, while in the trans-relativistic outflow model, one would expect a much flatter light curve of high-energy gamma-ray emission at early times, which could be dominated by both the SSC emission and the SNIC emission, depending on the properties of the underlying supernova and the shock parameter e and B . The Fermi Gamma-ray Space Telescope should be able to distinguish between the two models in the future.
118552679
Cosmic histories of star formation and reionization: an analysis with a power-law approximation
With a simple power-law approximation of high-redshift (3.5) star formation history, i.e., *(z)[(1+z)/4.5]??, we investigate the reionization of intergalactic medium (IGM) and the consequent Thomson scattering optical depth for cosmic microwave background (CMB) photons. A constraint on the evolution index ? is derived from the CMB optical depth measured by the Wilkinson Microwave Anisotropy Probe (WMAP) experiment, which reads ? ? 2.18 lg ??3.89, where the free parameter ? is the number of the escaped ionizing ultraviolet photons per baryon. At the same time, the redshift zf at which the IGM is fully ionized can also be expressed as a function of ? as well as ?. By further taking into account the implication of the Gunn-Peterson trough observations to quasars for the full reionization redshift, i.e., 6zf7, we obtain 0.3?1.3 and 80?230. For a typical number of ~ 4000 of ionizing photons released per baryon of normal stars, the fraction of these photons escaping from the stars, fesc, can be constrained to within the range of (2.0?5.8)%.
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.
115307247
E2/M1 ratio of the Delta gamma N transition within the chiral constituent quark model
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.
117386269
N phi states in a chiral quark model
The structures of N{phi} states with spin-parity J{sup p}=3/2{sup -} and J{sup p}=1/2{sup -} 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 channel coupling of N{phi} and {lambda}K{sup *} is considered, and the effect of the tensor force which results in the mixing of S and D waves is also investigated. The results show that the N{phi} state has an attractive interaction, and in the extended chiral SU(3) quark model such an attraction plus the channel coupling effect can consequently make for an N{phi} quasi-bound state with several MeV binding energy.
123526917
Multi-strange hadronic systems in a chiral SU(3) quark mean field model
We apply the chiral SU(3) quark mean field model to investigate the finite nuclei. We find that the combined confining potential chi(c)(C) is more proper to describe finite nuclei compared with the scalar and scalar-vector potentials. The hypernuclei and multi-strange objects which include A and Xi are discussed in this model. The maximum binding energy for such kind of multi-strange objects is about 16-17 MeV and the corresponding strangeness fraction f(s) is around 1.2-1.3. (C) 2002 Elsevier Science B.V. All rights reserved.