Broadband lightcurve characteristics of GRBs 980425 and 060218 and comparison with long-lag, wide-pulse GRBs

It has been recently argued that low-luminosity gamma-ray bursts (LL-GRBs) are likely a unique GRB population. Here, we present systematic analysis of the lightcurve characteristics from X-ray to gamma-ray energy bands for the two prototypical LL-GRBs 980425 and 060218. It is found that both the pulse width ($w$) and the ratio of the rising width to the decaying width ($r/d$) of theses two bursts are energy-dependent over a broad energy band. There exists a significant trend that the pulses tend to be narrower and more symmetry with respect to the higher energy bands for the two events. Both the X-rays and the gamma-rays follow the same $w - E$ and $r/d - E$ relations. These facts may indicate that the X-ray emission tracks the gamma-ray emission and both are likely to be originated from the same physical mechanism. Their light curves show significant spectral lags. We calculate the three types of lags with the pulse peaking time ($t_{peak}$), the pulse centroid time ($t_{cen}$), and the cross-correlation function (CCF). The derived $t_{peak}$ and $t_{cen}$ are a power-law function of energy. The lag calculated by CCF is strongly correlated with that derived from $t_{peak}$. But the lag derived from $t_{cen}$ is less correlated with that derived from $t_{peak}$ and CCF. The energy dependence of the lags is shallower at higher energy bands. These characteristics are well consistent with that observed in typical long-lag, wide-pulse GRBs, suggesting that GRBs 980425 and 060218 may share the similar radiation physics with them.Comment: 26 pages, 10 figures, 3 tables, accepted for publication in Ap

Two-component model for the chemical evolution of the Galactic disk

In the present paper, we introduce a two-component model of the Galactic disk to investigate its chemical evolution. The formation of the thick and thin disks occur in two main accretion episodes with both infall rates to be Gaussian. Both the pre-thin and post-thin scenarios for the formation of the Galactic disk are considered. The best-fitting is obtained through $\chi^2$-test between the models and the new observed metallicity distribution function of G dwarfs in the solar neighbourhood (Hou et al 1998). Our results show that post-thin disk scenario for the formation of the Galactic disk should be preferred. Still, other comparison between model predictions and observations are given.Comment: 23 pages, 7 figure

Maximal Entanglement of Two-qubit States Constructed by Linearly Independent Coherent States

In this paper, we find the necessary and sufficient condition for the maximal entanglement of the state, $|\psi>=\mu|\alpha>|\beta>+\lambda|\alpha>|\delta>+ \rho|\gamma>|\beta>+\nu|\gamma>|\delta>,$ constructed by linearly independent coherent states with \emph{real parameters} when $=$. This is a further generalization of the classified nonorthogonal states discussed in Ref. Physics Letters A {\bf{291}}, 73-76 (2001).Comment: some examples added; Int J Theor Phys 201

Exposure to hazardous volatile organic compounds, PM 10 and CO while walking along streets in urban Guangzhou, China

Toxic air pollutants in street canyons are important issues concerning public health especially in some large Asian cities like Guangzhou. In 1998 <18% of Guangzhou citizens used public transportation modes, with a majority commuting on foot (42%) or by bicycle (22%). Of the pedestrians, 57% were either senior citizens or students. In the present study, we measured toxic air pollutants while walking along urban streets in Guangzhou to evaluate pedestrian exposure. Volatile organic compounds (VOCs) were collected with sorbent tubes, and PM 10 and CO were measured simultaneously with portable analyzers. Our results showed that pedestrian exposure to PM 10 (with an average of 303 μg m -3 for all samples) and some toxic VOCs (for example, benzene) was relatively high. Monocyclic aromatic hydrocarbons were found to be the most abundant VOCs, and 71% of the samples had benzene levels higher than 30 μg m -3. Benzene, PM 10 and CO in walk-only streets were significantly lower (p<0.05) than in traffic streets, and the differences in exposure levels between new urban streets and old urban streets were highly significant (p<0.01). Pedestrian exposure to toxic VOCs and PM 10 was higher than those reported in other public transportation modes (bus and subway). The good correlations between BTEX, PM 10 and CO in the streets indicated that automotive emission might be their major source. Our study also showed that the risk to pedestrians due to air pollution was misinterpreted by the reported air quality index based on measurement of SO 2, NO x and PM 10 in the government monitoring stations. An urban roadside monitoring station might be needed by air quality monitoring networks in large Asian cities like Guangzhou, in order to survey exposure to air toxics in urban roadside microenvironments. © 2004 Elsevier Ltd. All rights reserved