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Title: Low-resolution VLT spectroscopy of GRBs 991216, 011211 and 021211
Authors: Vreeswijk, P. M.
Smette, A.
Ledoux, C.
Vreeswijk, P. M.
Rol, E.
Wijers, R. A. M. J.
Kaper, L.
Smette, A.
Smette, A.
Fruchter, A. S.
Palazzi, E.
Pian, E.
Masetti, N.
Frontera, F.
Rol, E.
O'Brien, P. T.
Wijers, R. A. M. J.
Kouveliotou, C.
Pian, E.
Frontera, F.
Hjorth, J.
Fynbo, J. P. U.
Jakobsson, P.
Watson, D.
Gorosabel, J.
Piro, L.
First Published: Feb-2006
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy & Astrophysics, 2006, 447 (1), pp. 145-156
Abstract: We present low-resolution VLT spectroscopy of the afterglow of the gamma-ray bursts (GRBs) 991216, 011211 and 021211. Our spectrum of GRB 991216 is the only optical spectrum for this afterglow. It shows two probable absorption systems at z=0.80 and z=1.02, where the highest redshift most likely reflects the distance to the host galaxy. A third system may be detected at z=0.77. HST imaging of the field, obtained 4 months after the burst, has resulted in the detection of two amorphous regions of emission, one at the projected afterglow position, and the other 0 $.\!\!^{\prime\prime}$6 away. The spectrum shows a depression in flux in between 4000 Å and 5500 Å. This could be the result of a 2175 Å-type extinction feature in the host of GRB 991216, but at a rather red wavelength of 2360 Å. If this interpretation is correct, it is the first time the extinction feature is seen in a GRB afterglow spectrum. It is centered at a wavelength similar to that of the ultra-violet (UV) bumps inferred from observations of a few UV-strong, hydrogen-poor stars in the Galaxy. All significant absorption lines (except for one) detected in the spectrum of GRB 011211 are identified with lines originating in a single absorption system at $z=2.142\pm0.002$, the redshift of the GRB 011211 host galaxy. We also detect the Ly$\alpha$ absorption line in the host, to which we fit a neutral hydrogen column density of log N( $\ion{H}{i}$) = $20.4\pm0.2$, which indicates that it is a damped Ly$\alpha$ system. Using a curve-of-growth analysis, we estimate the Si, Fe and Al metallicity at the GRB 011211 redshift to be [Si/H] = -0.9+0.6-0.4, $\rm [Fe/H]=-1.3\pm0.3$, and [Al/H] = -1.0+0.5-0.3. For GRB 021211, we detect a single emission line in a spectrum obtained tens of days after the burst, which we identify as [ $\ion{O}{ii}$] $\lambda$3727 at z=1.006. The corresponding unobscured [ $\ion{O}{ii}$] star-formation rate is 1.4 M$_{\odot}$ yr-1.
DOI Link: 10.1051/0004-6361:20053795
ISSN: 0004-6361
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2006 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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