Doppler effect of gamma-ray bursts in the fireball framework

The influence of the Doppler effect in the fireball framework on the spectrum of gamma-ray bursts is investigated. The study shows that the shape of the expected spectrum of an expanding fireball remains almost the same as that of the corresponding rest frame spectrum for constant radiations of the bremsstrahlung, Comptonized, and synchrotron mechanisms as well as for that of the GRB model. The peak flux spectrum and the peak frequency are obviously correlated. When the value of the Lorentz factor becomes 10 times larger, the flux of fireballs would be several orders of magnitude larger. The expansion speed of fireballs is a fundamental factor of the enhancement of the flux of gamma-ray bursts.Comment: 19 pages, 13 figure

Superfluidity and effective mass of magnetoexcitons in topological insulator bilayers: Effect of inter-Landau-level Coulomb interaction

The effective mass and superfluidity-normal phase transition temperature of magnetoexcitons in topological insulator bilayers are theoretically investigated. The intra-Landau-level Coulomb interaction is treated perturbatively, from which the effective magnetoexciton mass is analytically discussed. The inclusion of inter-Landau-level Coulomb interaction by more exact numerical diagonalization of the Hamiltonian brings out important modifications to magnetoexciton properties, which are specially characterized by prominent reduction in the magnetoexciton effective mass and promotion in the superfluidity-normal phase transition temperature at a wide range of external parameters.Comment: 5.6 EPL pages, 4 figure

Dependence of Temporal Properties on Energy in Long-Lag, Wide-Pulse Gamma-Ray Bursts

We employed a sample compiled by Norris et al. (2005, ApJ, 625, 324) to study the dependence of the pulse temporal properties on energy in long-lag, wide-pulse gamma-ray bursts. Our analysis shows that the pulse peak time, rise time scale and decay time scale are power law functions of energy, which is a preliminary report on the relationships between the three quantities and energy. The power law indexes associated with the pulse width, rise time scale and decay time scale are correlated and the correlation between the indexes associated with the pulse width and the decay time scale is more obvious. In addition, we have found that the pulse peak lag is strongly correlated with the CCF lag, but the centroid lag is less correlated with the peak lag and CCF lag. Based on these results and some previous investigations, we tend to believe that all energy-dependent pulse temporal properties may come from the joint contribution of both the hydrodynamic processes of the outflows and the curvature effect, where the energy-dependent spectral lag may be mainly dominated by the dynamic process and the energy-dependent pulse width may be mainly determined by the curvature effect.Comment: 20 pages, 7 figures, added references, matched to published version, accepted for publication in PAS

Probing crossover from analogous weak antilocalization to localization by an Aharonov-Bohm interferometer on topological insulator surface

We propose a scanning tunneling microscopy Aharonov-Bohm (AB) interferometer on the surface of a topological insulator (TI) to probe the crossover from analogous weak antilocalization (WAL) to weak localization (WL) phenomenon via the AB oscillations in spin-resolved local density of states (LDOS). Based on our analytical and numerical results, we show that with increasing the energy gap of TI surface states, the $\Phi_{0}/2$=$hc/2e$ periodic AB oscillations in spin-resolved LDOS gradually transit into the $\Phi_{0}$ periodic oscillations.Comment: 4.2 APL pages, 2 figure

Fractional quantum Hall effect of topological surface states under a strong tilted magnetic field

The fractional quantum Hall effect (FQHE) of topological surface-state particles under a tilted strong magnetic field is theoretically studied by using the exact diagonalization method. The Haldane's pseudopotentials for the Coulomb interaction are analytically obtained. The results show that by increasing the in-plane component of the tilted magnetic field, the FQHE state at $n$=0 Landau level (LL) becomes more stable, while the stabilities of $n$=$\pm1$ LLs become weaker. Moreover, we find that the excitation gaps of the $\nu=1/3$ FQHE states increase as the tilt angle is increased.Comment: 4.2 pages, 4 figure