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تسجيل مستخدم جديدGamma Ray Bursts Flares detected and observed by the Swift Satellite
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The detection of flares with the Swift satellite triggered a lot of bservational and theoretical interest in these phenomena. As a consequence a large analysis effort started within the community to characterize the phenomenon and at the same time a variety of theoretical speculations have been proposed to explain it. In this presentation we discuss part of the results we obtained analyzing a first statistical sample of GRBs observed with Swift. The first goal of this research is very simple: derive those observational properties that could distinguish between internal and external shock and between an ever active central engine and delayed shocks (refreshing) related to a very small initial Lorentz bulk factor. We discuss first the method of analysis and the morphology evidencing the similarities such flares have with the prompt emission pulses. We conclude that GRB flares are due to internal shocks and leave still open the question of whether or not the central engine is active for a time of the order of 105 seconds after the prompt emission.
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urred late relative to the ``prompt phase. Some remarkable flares are observed with fluence comparable to the prompt GRB fluence. Many GRBs have several flares, which are sometimes overlapping. Short, intense, repetitive, and late flaring can be most easily understood within the context of the standard fireball model with the internal engine that powers the prompt GRB emission in an active state at late times. However, other models for flares have been proposed. Flare origin can be investigated by comparing the flare spectra to that of the afterglow and the initial prompt emission. In this work, we have analyzed all significant X-ray flares from the first 110 GRBs observed by Swift. From this sample 33 GRBs were found to have significant X-ray flares, with 77 flares that were detected above the 3$sigma$ level. In addition to temporal analysis presented in a companion paper, a variety of spectral models have been fit to each flare. In some cases, we find that the spectral fits favor a Band function model, which is more akin to the prompt emission than to that of an afterglow. We find that the average fluence of the flares is 2.4e-7 erg/cm^2/s in the 0.2-10 keV energy band, which is approximately a factor of ten below the average prompt GRB fluence. These results, when combined with those presented in the companion paper on temporal properties of flares, supports the hypothesis that most X-ray flares are late-time activity of the internal engine that spawned the initial GRB; not an afterglow related effect.
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