Rotation of Polarization Angle in Gamma-Ray Burst Prompt Phase−-\uppercase\expandafter{\romannumeral2}. The Influence of The Parameters

In addition to the light curve and energy spectrum, polarization is also important for the study of Gamma-ray burst (GRB) prompt emission. Rotation of the polarization angle (PA) with time will cause depolarization of the time-integrated polarization degree. However, it is rarely studied before. Here, we use the magnetic reconnection model with a large-scale ordered aligned magnetic field in the emitting region to study the influence of the key parameters on the PA rotations. We find that half-opening angle of the jet $\theta_{j}$, the observational angle $\theta_{V}$, and the bulk Lorentz factor $\Gamma$ all have significant impacts on the PA rotations. For a fixed $\theta_{j}\Gamma_{0}$ value ($\Gamma_{0}$ is the normalization factor of $\Gamma$), regardless of concrete $\theta_{j}$ and $\Gamma_{0}$ values, PA rotation within $T_{90}$ ($\triangle$PA) remains roughly unchanged for a $q\equiv\theta_{V}/\theta_{j}$ value. As $\theta_{j}\Gamma_{0}$ value increases, the $q$ range for $\triangle$PA$>10^{\circ}$ becomes smaller. The most significant PA rotation with $\triangle$PA$\thicksim90^{\circ}$ will happen when $\theta_{j}\Gamma_{0}\thicksim100$ and $1.1\leq q\leq1.2$. For the top-hat jet, observations of the PA rotation within $T_{90}$ will imply a slightly off-axis observation.Comment: 9 pages, 7 figures, submitte

A systematic study on the binding energy of Λ\Lambda hypernuclei

In this paper, we calculated the binding energy per baryon of the $\Lambda$ hypernuclei systemically, using the relativistic mean field theory (RMF) in a statistic frame. Some resemble properties are found among most of the hypernuclei found in experiments. The data show that a $\Lambda$ hypernucleus will be more stable, if it is composed of a $\Lambda$ hyperon adding to a stable normal nuclear core, or a $\Lambda$ hyperon replacing a neutron in a stable normal nuclear core. According to our calculations, existences of some new $\Lambda$ hypernuclei are predicted under the frame of RMF.Comment: 8 pages, 6 figures, 3 table

Afterglow polarizations in a stratified medium with effect of the equal arrival time surface

The environment of gamma-ray burst (GRB) has an important influence on the evolution of jet dynamics and of its afterglow. Here we investigate the afterglow polarizations in a stratified medium with the equal arrival time surface (EATS) effect. Polarizations of multi-band afterglows are predicted. The effects of the parameters of the stratified medium on the afterglow polarizations are also investigated. We found the influences of the EATS effect on the afterglow polarizations become important for off-axis detections and PD bumps move to later times with the EATS effect. Even the magnetic field configurations, jet structure and observational angles are fixed, polarization properties of the jet emission could still evolve. Here, we assume a large-scale ordered magnetic field in the reverse-shock region and a two-dimensional random field in the forward-shock region. Then PD evolution is mainly determined by the evolution of $f_{32}$ parameter (the flux ratio between the reverse-shock region and forward-shock region) at early stage and by the evolution of the bulk Lorentz factor $\gamma$ at late stage. Through the influences on the $f_{32}$ or $\gamma$, the observational energy band, observational angles, and the parameters of the stratified medium will finally affect the afterglow polarizations.Comment: 16 pages, 8 figures, accepted by Ap

Cosmic age test in inhomogeneous cosmological models mimicking Λ\LambdaCDM on the light cone

The possibility of reconstructing a spherically symmetric inhomogeneous Lemaitre-Tolman-Bondi (LTB) model with $\Lambda$CDM observations has drawn a lot of attention. Recently, a LTB model having the same luminosity-distance and light-cone mass density as the $\Lambda$CDM model was reconstructed. We calculate the cosmic age at our position in this model, and get the age $t_{LTB}<11.7$Gyr in 2$\sigma$ confidence level from the Seven-Year WMAP observations. This result is inconsistent with some Milky Way observations.Comment: 6 pages, 1 figure