اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe afterglow onset for GRB060418 and GRB060607A
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Gamma-ray burst are thought to be produced by highly relativistic outflows. Although upper and lower limits for the outflow initial Lorentz factor $Gamma_0$ are available, observational efforts to derive a direct determination of $Gamma_0$ have so far failed or provided ambiguous results. As a matter of fact, the shape of the early-time afterglow light curve is strongly sensitive on $Gamma_0$ which determines the time of the afterglow peak, i.e. when the outflow and the shocked circumburst material share a comparable amount of energy. We now comment early-time observations of the near-infrared afterglows of GRB 060418 and GRB 060607A performed by the REM robotic telescope. For both events, the afterglow peak was singled out and allowed us to determine the initial fireball Lorentz, $Gamma_0sim 400$.
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We compared the time (or time limit) of onset for optical afterglow emission to the gamma-ray variability V in 76 GRBs with redshifts. In the subset (25 cases) with the rise evident in the data, we fit the shape of the onset peak as well and compared
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