The Studies Of Single Pulse Light Curves And Energy Spectra Of Gamma-ray Bursts

Gamma-ray burst (GRB) is a flash from space, with most energy in gamma-ray and with short duration. It is the most drastic burst since we observed. GRBs are first detected in 1967, and have been regarded as a great mystery since then. Although much progress has been made only within 30 years, many problems still puzzle us. In this thesis, I first present a brief review on both theories and observations of GRB, and then introduce some detailed works finished by my collaborators and me.Chapter 1-4 are the review of GRB. In Chapter 1, we introduce in detail some main instruments of GRB; We summarize the characteristic of GRB in four different phases in Chapter 2; In Chapter 3, we introduce the results of GRB theory; In Chapter 4, two issues associated with GRB are presented.Chapter 5-8 are my works on GRB single pulse light curves and energy spectra. In Chapter 5, we introduce Qin Doppler model, which is base of my first work.Chapter 6 is my work based on Qin model. A power law relationship between the pulse width and energy of GRBs was found by many authors. In this Chapter, we first introduce some results related to this work. Recently, under the assumption that the Doppler effect of the relativistically expanding fireball surface is important, Qin et al. showed that in most cases the mentioned power law relationship would exist in a certain energy range and within a similar range a power law relationship of an opposite trend between the ratio of the rising width to the decaying width and energy would be expectable for the same burst. We check this prediction with two GRB samples which contain well identified pulses. A power law anti-correlation between the full pulse width and energy and a power law correlation between the pulse width ratio and energy are seen in the light curves of the majority (around 65%) of bursts of the two samples within the energy range of BATSE, suggesting that these bursts are likely to arise from the emission associated with the shocks occurred on a relativistically expanding fireball surface. In addition, we find that the upper limits of the width ratio for the two samples do not exceed 0.9, in agrement with what predicted previously by the Doppler model. According to the distinct values of two power law indicesα_FWHM andα_ratio we divide the bursts into three subsets which are located in different areas of theα_FWHM -α_ratio plane. We suspect that different locations of (α_FWHM ,α_ratio) might correspond to different mechanisms.In Chapter 7, we investigate the relationship between the spectral lag and the pulse width. We focus on the relationships between relative spectral lags and relative widths of GRBs. The phenomenon of GRB spectral lags is very common. But the definite answer to this issue has not yet been given. Employing a sample consisting of 82 GRB pulses we find that the spectral lags are correlated with the pulse widths. However, there have no correlation between the relative spectral lags and the relative pulse widths. We suspect that the correlations between spectral lags and pulse widths might be caused by the Lorentz factor of the GRBs concerned. Our analysis on the relative quantities suggests that the intrinsic spectral lag might reflect other aspect of pulses than the aspect associated with the dynamical time of shocks or that associated with the time delay owing to the curvature effect.In Chapter 8, we study the spectral evolution of GRB single pulse. We investigate carefully the BATSE spectral sample analyzed by Kaneko et al. and find that there are some especial single pulses, whose spectral peak energy, E_peak, follow the evolution of soft-hard-soft. Therefore we select 82 well identified pulses whose E_peak follow soft-hard-soft evolution and study their evolution characteristics of E_peak. When we analyse these pulses as a whole, we find that: a) the E_peak follow indeed soft-hard-soft evolution; b) the fore phase of soft-hard is shorter than the back phase of hard-soft; c) the softest spectra of back phase are much softer than the softest spectra of fore phase; d) the spectra of fore phase are harder than 100 keV and the back phase are harder than 50 keV but some are softer than 100 keV, which are consistent with current view on the generation of GRBs. When we classify these pulses into type I (the rise widths are less than the decay widths) and type II (the rise widths are larger than the decay widths) according to their profiles, we only find that the fore phase of type II are much longer than the back phase. The other characteristics are consistent. We suspect that the type I and type II might be related to the different process of internal shock. Type I might be result from forward shock, while the type II might be come from reverse shock, which deserve the further investigation.Finally, we present a summary of the open questions and prospects in the current GRB research field in Chapter 9.