| Gamma-Ray Bursts (GRBs) are produced at deep universe due to death of massive star or merger of compact objects with extremely relativistic jets. But the composition of jet and its radiation process are still unknown today. This thesis reviews the observation and theory survey of GRBs and focuses on the composition and emission spectral component of fireball based on Swift observation.When Burst-Alert-Telescope (BAT) on board Swift is triggered by a GRB source, X-ray Telescope (XRT) slews to observe it rapidly. So much x-ray observation data are collected, especially bright XRT-BAT flares of some bursts are detected. Then we make a combined spectral analysis on29bright XRT-BAT flares in our sample.8flares are well modeled by Power-law,10flares are Band and the rest11flares favor the single Power-law plus Blackbody model. The results show that some bursts have evolved to low energy and some Ep are still beyond the BAT energy band.Making use of the thermal emission in our sample with measurement redshift, In baryonic fireball scenario, we derive the fireball quantities, including photospheric Lorentz factor Γph, photospheric radius Rph, saturation radius Rs, and initial radius R0. The Ep-LBB relation from thermal emission is well consistent with Ep-LBB from Band function. The Γph-LBB from thermal emission in our sample is also consistent with previous Γph-LBB.from the deceleration time. The results support the GRBs thermal component is from photospheric emission of a baryonic fireball. As thermal emission component with a relative low temperature is detected only in a small fraction bursts, so the composition of GRBs fireball may be diverse. For GRB090902B with a dominated thermal emission, it is maybe a baryonic fireball. If the photospheric temperature is low, i.e. our sample, the thermal component is much weaker(～5%). These bursts may be moderate magnetized. Most GRBs are highly magnetized fireball and the thermal components are suppressed. |
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