Extended Emission of Short Gamma-Ray Bursts

Preliminary results of our analysis on the extended emission of short/medium duration GRBs observed with Swift/BAT are presented. The Bayesian blocks algorithm is used to analyze the burst durations and the temporal structure of the lightcurves in different energy bands. We show here the results of three bursts (GRBs 050724, 061006 and 070714B) that have a prominent soft extended emission component in our sample. The extended emission of these bursts is a continuous, flickering-liked component, lasting $\sim 100$ seconds post the GRB trigger at 15-25 keV bands. Without considering this component, the three bursts are classified as short GRBs, with $T_{90}=2\sim 3$ seconds. GRB 060614 has an emission component similar to the extended emission, but this component has pulse-liked structure, possibly indicating that this emission component is different from that observed in GRBs 050724, 061006, and 070714B. Further analysis on the spectral evolution behavior of the extended emission component is on going.Comment: 2008 Nanjing GRB Conferenc

Mass-Transfer Process of Galactic Compact Binaries

In this paper we focus on the effect of mass transfer between compact binary stars like neutron star-neutron star (NS-NS) system and neutron star-white dwarf (NS-WD) system. We adopt mass quadrupole formula with post-Newtonian approximation to calculate the gravitational wave (GW) radiation and orbit evolution. Two kinds of mass transfer process are considered here. One is the tidal disruption model where the less dense star orbits into the Roche limit and its mass flows toward to the other star as a beam of incompressible fluid, and the other is common envelope model where we divide the transferring mass into the mass-inflow of envelope and the the envelope itself winding in the Roche lobe of the binary stars. Viewing the envelope as a background, the GW by its spin can be calculated as a pulsar. Assuming a mass-inflow parameter, we eventually obtain the radiation power and corrected gravitational wave form (GWF) templates for different initial mass ratios, which are mainly captured by the inspiral duration and strain and of the GWs.Comment: 11 page

Thermodynamical and dynamical properties of Charged BTZ Black Holes

We investigate the spacetime properties of BTZ black holes in the presence of the Maxwell field and Born-Infeld field and find rich properties in the spacetime structures when the model parameters are varied. Employing the Landau-Lifshitz theory, we examine the thermodynamical phase transition in the charged BTZ black holes. We further study the dynamical perturbation in the background of the charged BTZ black holes and find different properties in the dynamics when the thermodynamical phase transition occurs.Comment: Version accepted by EPJ

Multiphase transport model for heavy ion collisions at RHIC

Using a multiphase transport model (AMPT) with both partonic and hadronic interactions, we study the multiplicity and transverse momentum distributions of charged particles such as pions, kaons and protons in central Au+Au collisions at RHIC energies. Effects due to nuclear shadowing and jet quenching on these observables are also studied. We further show preliminary results on the production of multistrange baryons from the strangeness-exchange reactions during the hadronic stage of heavy ion collisions.Comment: 4 pages, 4 figures, espcrc1.sty included, presented at 15th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (QM2001), Long Island, New York, January 200

Phases of (2+1)D SO(5) non-linear sigma model with a topological term on a sphere: multicritical point and disorder phase

Novel critical phenomena beyond the Landau-Ginzburg-Wilson paradigm have been long sought after. Among many candidate scenarios, the deconfined quantum critical point (DQCP) constitutes the most fascinating one, and its lattice model realization has been debated over the past two decades. Here we apply the spherical Landau level regularization upon the exact (2+1)D SO(5) non-linear sigma model with a topological term to study the potential DQCP therein. Utilizing the state-of-the-art density matrix renormalization group method with explicit $\text{SU(2)}_\text{spin}\times\text{U(1)}_\text{charge}$ symmetries, accompanied by quantum Monte Carlo simulation, we accurately obtain the comprehensive phase diagram of the model on a sphere with unprecedentedly large system sizes. We find various novel quantum phases, including a N\'eel state, a ferromagnet (FM), a valence bond solid (VBS) state, a valley polarized (VP) state and quantum disordered phase occupying extended area of the phase diagram. However, notably missing in the phase diagram is the DQCP between different symmetry-breaking phases. Instead, our results show that two different symmetry-breaking phases, i.e., the SO(2)-breaking VBS and the SO(3)-breaking N\'eel states, are separated by either a weakly first-order transition or the disordered region with a multicritical point in between, thus opening up more interesting questions on this two-decade long debate on the nature of DQCP.Comment: 20 pages, 15 figure

Exploring Anisotropic Lorentz Invariance Violation from the Spectral-Lag Transitions of Gamma-Ray Bursts

The observed spectral lags of gamma-ray bursts (GRBs) have been widely used to explore possible violations of Lorentz invariance. However, these studies were generally performed by concentrating on the rough time lag of a single highest-energy photon and ignoring the intrinsic time lag at the source. A new way to test nonbirefringent Lorentz-violating effects has been proposed by analyzing the multi-photon spectral-lag behavior of a GRB that displays a positive-to-negative transition. This method gives both a plausible description of the intrinsic energy-dependent time lag and comparatively robust constraints on Lorentz-violating effects. In this work, we conduct a systematic search for Lorentz-violating photon dispersion from the spectral-lag transition features of 32 GRBs. By fitting the spectral-lag data of these 32 GRBs, we place constraints on a variety of isotropic and anisotropic Lorentz-violating coefficients with mass dimension $d=6$ and $8$. While our dispersion constraints are not competitive with existing bounds, they have the promise to complement the full coefficient space.Comment: 17 pages, 2 figures, 2 tables. Published by Universe. Constribution to the Special Issue "Advances in Astrophysics and Cosmology-in Memory of Prof. Tan Lu