D'Elia 2008 GRB 080319B的高分辨谱

主要内容:
余辉阶段的谱，有多个成分，可能是外部介质环境的吸收

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文章信息:

· arXiv e-print (arXiv:0804.2141)

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Title:		The prompt, high resolution spectroscopic view of the "naked-eye" GRB080319B
Authors:		D'Elia, V.; Fiore, F.; Perna, R.; Krongold, Y.; Covino, S.; Fugazza, D.; Lazzati, D.; Nicastro, F.; Antonelli, L. A.; Campana, S.; Chincarini, G.; D'Avanzo, P.; Della Valle, M.; Goldoni, P.; Guetta, D.; Guidorzi, C.; Meurs, E. J. A.; Molinari, E.; Norci, L.; Piranomonte, S.; Stella, L.; Stratta, G.; Tagliaferri, G.; Ward, P.
Publication:		eprint arXiv:0804.2141
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		5 pages, 4 .ps figures, ApJL, submitted
Bibliographic Code:		2008arXiv0804.2141D

Abstract

GRB080319B reached 5th optical magnitude during the burst. Thanks to the VLT/UVES rapid response mode, we observed its afterglow just 8m:30s after the GRB onset when the magnitude was R ~ 12. This allowed us to obtain the best signal-to-noise, high resolution spectrum of a GRB afterglow ever (S/N per resolution element ~ 50). The spectrum is rich of absorption features belonging to the main system at z=0.937, divided in at least six components spanning a total velocity range of 100 km/s. The VLT/UVES observations caught the absorbing gas in a highly excited state, producing the strongest Fe II fine structure lines ever observed in a GRB. A few hours later the optical depth of these lines was reduced by a factor of 4-20, and the optical/UV flux by a factor of ~ 60. This proves that the excitation of the observed fine structure lines is due to ``pumping'' by the GRB UV photons. A comparison of the observed ratio between the number of photons absorbed by the excited state and those in the Fe II ground state suggests that the six absorbers are $\gs18-34$ kpc from the GRB site, with component I ~ 2 times closer to the GRB site than components III to VI. Component I is characterized also by the lack of Mg I absorption, unlike all other components. This may be due to a higher gas temperature, suggesting a structured ISM in this galaxy complex.

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