The Light Curves And The Spectral Harness Ratios Of Gamma-Ray Bursts

We summarize the observational and theoretical studies of gamma-ray bursts (GRBs), and present the results of our studies on the statistical properties of the light curves and the spectral hardness ratios of GRBs.We study the statistical properties of the pulses in GRB temporal profiles using 2044 burst data detected by BATSE on board CGRO with a wavelet package analysis technique and a developed pulse-finding algorithm. Our results are as following:(l)We presented the distributions of the width, intensity, and ratios of rise-to-decay of pulses, and found these properties of pulses are varied from burst to burst. (2)We presented the average curves of emissivity (ACEs) of pulses by a beginning-aligned method, and analyzed the relations between then- shape parameters and energy. We found that the width, the rising time scale, and the decaying time scale decay with energy with a power law. However, their peakness and ratio of rise-to-decay are exponential increase with energy. The relation between pulse width and energy are consistent with the result of synchrotron emission. (3)We studied the characteristic structures of pulses in different channels by a duration-and-fluence-normalized method, and found that the characteristic structures of pulses in four channels are the same. (4)We investigated the difference of the ACEs of the long and short GRBs. The results show that the ACEs of pulses in two groups have a significant difference. The ACEs of the pulses in short group are shorter and narrower than that in long group, suggesting that the cooling timescale of the relativistic electrons in short bursts are shorter than that in long bursts. The short bursts may emit more higher energy photons than that in the long bursts. The result is quite consistent with the well-known anti-correlation between hardness ratio (HR) and burst duration. The sources of them likely have intrinsic difference. Compared to the ACEs, the normalized ACEs of the pulses in the two groups seem to be similar. This suggests that the emission mechanisms are the same hi the two groups of bursts.We systematically studied statistical properties of the HR of GRBs. (1)We further confirmed the anti-correlation between HR and duration and pointed out that it is caused bythe different distributions of the two quantities in the two groups. This anti-correlation does not exist in each groups. We also proposed a more accurate interpretation of this anti-correlation, i.e., the shorter bursts tend to be harder, and the softer bursts tend to be longer. (2)We studied correlation between the total fluence and HR. We found a new evidence that is consistent with the classification of the long and short GRBs, and found that the total fluence is not correlated with HR in the entire set, but it is in each subsets. (3)We investigated the correlations between various HRs and reached conclusions that the slope of the higher part of the spectrum of most GRBs is independent of that of the lower part; emissions at higher energy bands from the bursts of both short- and long-duration classes are significantly different for different sources, but radiations at lower energy bands are similar; the spectra of the short-duration bursts is harder than that of the long-duration bursts. (4)We presented defines of HRs of high energy band and low energy bands, and presented the result of correlation studies, examining the association between the hardness ratios and the spectral fitting parameters. We found that the break energy(or peak energy) are correlated with the HRs in high and low energy bands. The spectral index of high energy band only correlated with the HRs of high energy band. The spectral index of low energy band is not correlated with any hardness ratios. (5)We also presented a define of time-resolved HR to study the evolution of HR during a burst. The results show that the average HR monotonously decreases with time. There are 77% of GRBs showing "hard-to-soft" evolutional feature, the rest showing "soft-to-hard" evolutional feature. We also found that th...