TheGRB afterglow onset observed byREM: fireball Lorentz factor and afterglow fluence
نویسندگان
چکیده
We report observations of the early light curves of GRB060418 and GRB060607A, carried out with the pink robotic telescope REM. A clear peak is detected for both events, which is interpreted as the onset of the afterglow, that is the time at which the fireball starts decelerating. This detection allows to directly measure the initial fireball Lorentz factor, which was found to be Γ0 ≈ 400 for both events, fully confirming the ultrarelativistic nature of gamma-ray burst fireballs. Sampling the light curve before the peak also allows to compute the bolometric fluence of the afterglow, which is 16% of the prompt one in the case of GRB060418.
منابع مشابه
REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination
Context. Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Aims. Currently, only lower limits were securely set to the initial fireball Lorentz factor Γ0. We aim to provide a direct measure of Γ0. Methods. The early-time afterglow light curve carries information about Γ0, which determines the time of the afterglow peak. We have obtained early observations...
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