Hascoët, R. 2011 "裸暴"可能并不裸

主要内容:
“裸暴”是没有余辉的暴，一般认为是外部介质密度非常低，所以叫裸暴。
文章讨论了如果密度非常高，也会看不到余辉。

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Title:		Was the "naked burst" GRB 050421 really naked?
Authors:		Hascoët, R.; Uhm, Z. L.; Mochkovitch, R.; Daigne, F.
Affiliation:		AA(Institut d'Astrophysique de Paris, UMR 7095 Université Pierre et Marie Curie-Paris 6 - CNRS, 98 bis boulevard Arago, 75014, Paris, France hascoet@iap.fr), AB(Institut d'Astrophysique de Paris, UMR 7095 Université Pierre et Marie Curie-Paris 6 - CNRS, 98 bis boulevard Arago, 75014, Paris, France), AC(Institut d'Astrophysique de Paris, UMR 7095 Université Pierre et Marie Curie-Paris 6 - CNRS, 98 bis boulevard Arago, 75014, Paris, France mochko@iap.fr)
Publication:		Astronomy & Astrophysics, Volume 534, id.A104 (A&A Homepage)
Publication Date:		10/2011
Origin:		EDP Sciences
Astronomy Keywords:		radiation mechanisms: non-thermal, gamma-ray burst: general, gamma-ray burst: individual: GRB 050421, shock waves
DOI:		10.1051/0004-6361/201117404
Bibliographic Code:		2011A&A...534A.104H

Abstract

Context. A few long gamma-ray bursts such as GRB 050421 show no afterglow emission beyond the usual initial steep decay phase. It has been suggested that these events correspond to "naked" bursts that occur in a very low density environment. We reconsider this possibility in the context of various scenarios for the origin of the afterglow. 
Aims: In the standard model where the afterglow results from the forward shock as well as in the alternative model where the afterglow comes from the reverse shock, we aim to obtain constraints on the density of the environment, the microphysics parameters, or the Lorentz factor of the ejecta, which are imposed by the absence of a detected afterglow. 
Methods: For the two models we compute the afterglow evolution for different values of the external density (uniform or wind medium) and various burst parameters. We then compare our results to the Swift data of GRB 050421, which is the best example of a long burst without afterglow. 
Results: In the standard model we show that consistency with the data imposes that the external density does not exceed 10^-5 cm^-3 or that the microphysics parameters are very small with ɛ_e ≲ 10^-2 and ɛ_B ≲ 10^-4. If the afterglow is caused by the reverse shock, we find that its contribution can be strongly reduced if the central source has mainly emitted fast-moving material (with less than 10-30% of the kinetic energy at Γ < 100) and was located in a dense environment. 
Conclusions: The two considered scenarios therefore lead to opposite constraints on the circumburst medium. The high-density environment, favored by the reverse shock model, better corresponds to what is expected if the burst progenitor was a massive star.

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