Conversion of neutron stars to strange stars as a possible origin of γ-ray bursts

We propose that some neutron stars in low-mass x-ray binaries can accrete sufficient mass to undergo a phase transition to become strange stars. The energy released per conversion event satisfies the requirements of cosmological y-ray bursts, and the Lorentz factor of the resultant expanding fireball may exceed 5 × 103 because the strange star has very low baryon contamination. The model burst rate is consistent with observations.published_or_final_versio

On the bimodal magnetic field distribution of binary pulsars

We combine the idea of movement of magnetic flux tubes in the stellar interiors with the analysis of crustal physics of accreting neutron stars in low- and high-mass X-ray binaries to explain the bimodal magnetic field distribution of binary pulsars. We propose that this distribution may result from different crustal properties of neutron stars with different accretion rates and amounts of accreted matter. In addition, we may provide an explanation for why the magnetic field strengths of millisecond pulsars with low-mass companions saturate at ∼3 × 10 8 G when accreted mass exceeds ∼0.5 M ⊙. © 1997. The American Astronomical Society. All rights reserved.published_or_final_versio

Are soft γ-ray repeaters strange stars?

The soft γ-ray repeaters (SGRs) are proposed to result from young, magnetized strange stars with superconducting cores. As such a strange star spins down, the quantized vortex lines move outward and drag the magnetic flux tubes because of the strong coupling between them. Since the terminations of the tubes interact with the stellar crust, the dragged tubes can produce sufficient tension to crack the crust and pull parts of the broken platelet into the quark core. The deconfinement of crustal matter into strange quark matter will release energy. The model burst energy, duration, time interval, spectrum, and the persistent x-ray emission from SGRs are shown to be in agreement with observed results.published_or_final_versio

Properties of nuclei in the inner crusts of neutron stars in the relativistic mean-field theory

We study the properties of nuclei in the inner crusts of neutron stars based on the Boguta-Bodmer nonlinear model in the relativistic mean-field theory. We carefully determine the surface diffuseness of the nuclei as the density of matter increases. The imaginary time step method is used to solve the Euler-Lagrange equation derived from the variational principle applied to the semiclassical energy density. It is shown that with increasing density, the spherical nuclei become more neutron rich and eventually merge to form a uniform liquid of neutrons, protons, and electrons. We find that the smaller the value of the incompressibility K, the lower the density at which the phase transition to uniform matter occurs. The relativistic extended Thomas-Fermi method is generalized to investigate nonspherical nuclei. Our results show that the spherical nucleus phase is the only equilibrium state in the inner crusts of neutron stars.published_or_final_versio

Measuring dark energy with the Eiso–Ep correlation of gamma-ray bursts using model-independent methods

We use two model-independent methods to standardize long gamma-ray bursts (GRBs) using the Eiso − Ep correlation (log Eiso = a + blog Ep), where Eiso is the isotropic-equivalent gamma-ray energy and Ep is the spectral peak energy. We update 42 long GRBs and attempt to constrain the cosmological parameters. The full sample contains 151 long GRBs with redshifts from 0.0331 to 8.2. The first method is the simultaneous fitting method. We take the extrinsic scatter σext into account and assign it to the parameter Eiso. The best-fitting values are a = 49.15 ± 0.26, b = 1.42 ± 0.11, σext = 0.34 ± 0.03 and Ωm = 0.79 in the flat ΛCDM model. The constraint on Ωm is 0.55 < Ωm< 1 at the 1σ confidence level. If reduced χ2 method is used, the best-fit results are a = 48.96 ± 0.18, b = 1.52 ± 0.08, and Ωm = 0.50 ± 0.12. The second method uses type Ia supernovae (SNe Ia) to calibrate the Eiso − Ep correlation. We calibrate 90 high-redshift GRBs in the redshift range from 1.44 to 8.1. The cosmological constraints from these 90 GRBs are Ωm = 0.23+0.06-0.04 for flat ΛCDM and Ωm = 0.18 ± 0.11 and ΩΛ = 0.46 ± 0.51 for non-flat ΛCDM. For the combination of GRB and SNe Ia sample, we obtain Ωm = 0.271 ± 0.019 and h = 0.701 ± 0.002 for the flat ΛCDM and the non-flat ΛCDM, and the results are Ωm = 0.225 ± 0.044, ΩΛ = 0.640 ± 0.082, and h = 0.698 ± 0.004. These results from calibrated GRBs are consistent with that of SNe Ia. Meanwhile, the combined data can improve cosmological constraints significantly, compared to SNe Ia alone. Our results show that the Eiso − Ep correlation is promising to probe the high-redshift Universe.published_or_final_versio

Development of a commercial induction cooker

Author name used in this publication: Y. LuAuthor name used in this publication: K. W. E. ChengAuthor name used in this publication: K. W. ChanAuthor name used in this publication: S. W. ZhaoRefereed conference paper2008-2009 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

Chemical heating in strange stars

As a strange star spins down, its core density increases, changing the chemical equilibrium state of strange matter. The relaxation toward the new equilibrium state takes a finite time, so the matter is not quite in chemical equilibrium, and energy is released by reactions at the expense of the stored chemical energy. We study such a chemical heating process for a spin-down strange star and find that this effect is significant at later times for weak magnetic fields. We compare the cooling of a strange star with that of an ordinary neutron star and find that the surface temperature of the strange star is much lower than that of the neutron star at the age up to 10 8 yr. This favorable to an observational signature for strange stars. © 1996. The American Astronomical Society. All rights reserved.published_or_final_versio

Properties of neutron stars in the relativistic mean-field theory

We study the properties of dense matter in neutron stars and calculate the structure of the stars based on the Zimanyi & Moszkowski (ZM) model in the relativistic mean-field theory. We also compare these results with those based on the Boguta (BB) model with a recent satisfactory parameter set. The two models satisfy the requirements from the observations of the masses of binary radio pulsars, the rotation frequencies of millisecond pulsars, the redshifts of the e + annihilation lines of some y-ray bursts if they are neutron stars, and the crustal moment of inertia of neutron stars deduced from the glitch events. Other observations may provide a way to discriminate between the two models. We suggest that the most important observational discriminant between these two models is found by observing the surface radiation of neutron stars, since the BB model leads to a large photon fraction of neutron star matter and rapid cooling of neutron stars, but the ZM model does not. © 1996. The American Astronomical Society. All rights reserved.published_or_final_versio

What do γ\gamma-ray bursts look like?

There have been great and rapid progresses in the field of $\gamma$-ray bursts (denoted as GRBs) since BeppoSAX and other telescopes discovered their afterglows in 1997. Here, we will first give a brief review on the observational facts of GRBs and direct understanding from these facts, which lead to the standard fireball model. The dynamical evolution of the fireball is discussed, especially a generic model is proposed to describe the whole dynamical evolution of GRB remnant from highly radiative to adiabatic, and from ultra-relativistic to non-relativistic phase. Then, Various deviations from the standard model are discussed to give new information about GRBs and their environment. In order to relax the energy crisis, the beaming effects and their possible observational evidences are also discussed in GRB's radiations.Comment: 10 pages, Latex. Invited talk at the Pacific Rim Conference on Stellar Astrophysics, Hong Kong, China, Aug. 199

Analysis of the masses and decay constants of the heavy-light mesons with QCD sum rules

In this article, we calculate the contributions of the vacuum condensates up to dimension-6 including the $${\mathcal {O}}(\alpha _s)$$ corrections to the quark condensates in the operator product expansion, then we study the masses and decay constants of the pseudoscalar, scalar, vector, and axial-vector heavy-light mesons with the QCD sum rules in a systematic way. The masses of the observed mesons $$(D,D^*)$$, $$(D_s,D_s^*)$$, $$(D_0^*(2400),D_1(2430))$$, $$(D_{s0}^*(2317),D_{s1}(2460)),$$ $$(B,B^*)$$, $$(B_s,B_s^*)$$ can be well reproduced, while the predictions for the masses of $$(B^*_{0}, B_{1})$$ and $$(B^*_{s0}, B_{s1})$$ can be confronted with the experimental data in the future. We obtain the decay constants of the pseudoscalar, scalar, vector, and axial-vector heavy-light mesons, which have many phenomenological applications in studying the semi-leptonic and leptonic decays of the heavy-light mesons