Gamma-ray bursts (GRBs) are currently believed to originate from highly magnetized, rapidly rotating compact objects. After the GRB, such an object may directly lose its rotational energy through some magnetically-driven processes, which produce an ultrarelativistic wind dominated possibly by the energy flux of electron-positron pairs. The interaction of this wind with an outward-expanding fireball leads to a relativistic wind bubble. Here we discuss the effects of this wind bubble. We find that when the wind energy significantly exceeds the initial energy of the fireball, the bulk Lorentz factor of the wind bubble decays more slowly than before, and more importantly, the reverse-shock emission could dominate the afterglow emission, which yields a bump in afterglow light curves.
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