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Low-resolution VLT spectroscopy of GRBs 991216, 011211 and 021211 | | P.M. Vreeswijk
; A. Smette
; A.S. Fruchter
; E. Palazzi
; E. Rol
; R.A.M.J. Wijers
; C. Kouveliotou
; L. Kaper
; E. Pian
; N. Masetti
; F. Frontera
; J. Hjorth
; J. Gorosabel
; L. Piro
; J.P.U. Fynbo
; P. Jakobsson
; D. Watson
; P.T. O’Brien
; C. Ledoux
; | | Date: |
13 Oct 2005 | | Abstract: | We present low-resolution VLT spectroscopy of the afterglow of the gamma-ray bursts (GRBs) 991216, 011211 and 021211. Our spectrum of GRB991216 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 0.6" away. The spectrum shows a depression in flux in between 4000 A and 5500 A. This could be the result of a 2175 A-type extinction feature in the host of GRB991216, but at a rather red wavelength of 2360 A. 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 GRB011211 are identified with lines originating in a single absorption system at z=2.142+/-0.002, the redshift of the GRB011211 host galaxy. We also detect the Lyman alpha absorption line in the host, to which we fit a neutral hydrogen column density of log N(HI)=20.4+/-0.2, which indicates that it is a damped Lyman alpha system. Using a curve-of-growth analysis, we estimate the Si, Fe and Al metallicity at the GRB011211 redshift. For GRB021211, we detect a single emission line in a spectrum obtained tens of days after the burst, which we identify as [OII] 3727 at z=1.006. The corresponding unobscured [OII] star-formation rate is 1.4 Msun/yr. | | Source: | arXiv, astro-ph/0510404 | | Services: | Forum | Review | PDF | Favorites | |
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