[vsnet-grb-info 11014] GRB 111008A: VLT/X-shooter spectroscopy

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12431
SUBJECT: GRB 111008A: VLT/X-shooter spectroscopy
DATE:    11/10/09 11:03:04 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

K. Wiersema (Univ. Leicester), H. Flores (GEPI/Obs. de Paris), V. D'Elia 
(ASI/ASDC & INAF/OAR), P. Goldoni (APC/Univ. Paris 7 & SAp/CEA), D. 
Malesani (DARK/NBI), S. D. Vergani (INAF/OABr), A. de Ugarte Postigo 
(IAA-CSIC), A. J. Levan (Univ. Warwick), B. Milvang-Jensen, J. P. U. 
Fynbo (DARK/NBI), report on behalf of a larger collaboration:

We observed the optical counterpart of GRB 111008A (Saxton et al., GCN 
12423; Levan et al., GCN 12426; Xu et al., GCN 12427; Nardini et al., 
GCN 12428), using the X-shooter spectrograph mounted on the ESO-VLT. 
Observations started on 2011 October 9.247 UT (7.71 hr after the GRB), 
with a total exposure time of 2 hr, covering the wavelength range 
3000-25000 AA.

Continuum is clearly detected  redwards of ~7600 AA, with several, 
strong superimposed absorption features, consistent with a commom 
redshift z = 4.9898. Among them, we note several Si II and Fe II 
transitions, the CIV doublet, the Mg II doublet (in the H band), and 
several fine-structure lines commonly observed in GRB afterglow spectra 
(such as Si II*, S II*, O I*). We also note the presence of an 
intervening Mg II system at z = 4.61. Our results are thus consistent 
with the redshift derived by Levan et al. (GCN 12429; see also Nardini 
et al., GCN 12428).

We acknowledge excellent support from the observing staff in Paranal, in 
particular Christophe Martayan, Claudio Melo, Leonel Rivas, and Sergio Vera.