Chen2006 GRB余辉的谱中无WR星的信息

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astro-ph/0611079 [abs, ps, pdf, other] :

Title: On the absence of Wolf-Rayet Signatures in GRB Afterglow Spectra: Constraints on the GRB Progenitor Environment
Authors: Hsiao-Wen Chen (U of Chicago), Jason X. Prochaska (UCO/Lick Observatory), Josha S. Bloom (UC Berkeley), Enrico Ramirez-Ruiz (IAS), Miroslava Dessauges-Zavadsky (Geneva Observatory), Ryan J. Foley (UC Berkeley)
Comments: 22 pages, including 13 figures; submitted to ApJ; a complete version with higher-resolution figures is available at this http URL

(Abridged) We carry out a systematic search in a sample of five afterglow spectra for Wolf-Rayet wind signatures, as represented by blue-shifted, high-velocity (|\Delta v| = 1000-5000 km/s CIV 1548, 1550 absorption doublets (designated as CIV_{15}). We report the detection of a CIV_{15} absorber at \Delta v ~ -1500 km/s for GRB 050730 and none in the rest of the sample. Our search yields an estimate of ~20% for the incidence of CIV_{15} absorbers with rest-frame absorption equivalent width of EW(1548)>0.2 Ang from the GRB host galaxies. This is consistent with the incidence of CIV_{15} around classical damped Lya absorbers toward quasar sightlines, and suggests that the majority of CIV_{15} absorbers originate in foreground galaxies. We first demonstrate that the presence of associated HI 1215, CII 1334, or SiII 1260 absorption argues against a CSM origin. The absence of fine-structure absorption such as CII or SiII* further rules out the progenitor-CSM hypothesis, because it indicates negligible UV pumping. The lack of Wolf-Rayet features is consistent with the expectation that the circumburst medium is fully ionized by the afterglow radiation field. The null result therefore constrains the extent of free expanding winds, which we estimate <>