TITLE:   GCN CIRCULAR
NUMBER:  10971
SUBJECT: GRB 100724A: X-shooter redshift
DATE:    10/07/24 06:55:35 GMT
FROM:    Antonio Deugarte at IAA-CSIC  <deugarte@iaa.es>

C. C. Thoene, A. de Ugarte Postigo (INAF-OAB), P. Vreeswijk (Univ.
Iceland), P. D'Avanzo, S. Covino (INAF-OAB), J. P. U. Fynbo (DARK/NBI) and
N. Tanvir (Univ. Leicester) report on behalf of the X-shooter
collaboration

We observed the optical afterglow of GRB 100724A (Markwardt et al., GCN
10968, Olivares et al., GCN 10969, 10970) with X-shooter at the VLT in RRM
mode on July 24, 2010, starting at 00:53 UT (11 min after the burst).

We detect several absorption lines including Fe II 2344, 2383, 2586, 2600,
the Mg II doublet (2796, 2803) and Mg I 2852 at a common redshift of 1.288
which we suggest to be the redshift of the GRB. The wavelength calibration
was obtained from archival files and is therefore considered preliminary.

We thank the Paranal staff for performing the observations, in particular
Lorenzo Monaco and Andres Pino.