Malesani 2007 GRB 060418 and GRB 060607A的早期余辉观测

主要内容:
给出了用REM对GRB 060418 and GRB 060607A的早期余辉观测，估算早期的Lorentz因子有400。而余辉的流量有暴本身的16%，对GRB 060418来说的话。

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文章信息:
arXiv:0706.1772 [ ps, pdf, other] : Title: The GRB afterglow onset observed by REM: fireball Lorentz factor and afterglow fluence
Authors: Daniele Malesani (DARK), Emilio Molinari (INAF/Brera), Susanna Vergani (DIAS and DCU), Stefano Covino (INAF/Brera), for the REM team
Comments: 4 pages, 1 figure, to appear in New Astronomy Reviews, proceedings of "070228: The Next Decade of Gamma-Ray Burst Afterglows", Amsterdam, 2007 March 19-23, eds. R.A.M.J. Wijers, L. Kaper, E. van Eerten

We report observations of the early light curves of GRB 060418 and GRB 060607A, 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 Gamma_0 ~ 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 GRB 060418.