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GCN Circular 10876

GRB 100621A: VLT/X-shooter redshift
2010-06-21T14:00:38Z (14 years ago)
Bo Milvang-Jensen at Dark Cosmology Centre,NBI,U. Copenhagen <>
B. Milvang-Jensen (DARK/NBI), P. Goldoni (APC/Univ. Paris 7 and SAp/CEA),
N. R. Tanvir, K. Wiersema (Univ. Leicester), D. Malesani (DARK/NBI),
A. de Ugarte Postigo (INAF-OAB), V. D'Elia (INAF-OAR and ASDC),
S. D. Vergani (GEPI/Obs. Paris and APC/Univ. Paris 7),
J. P. U. Fynbo (DARK/NBI), L. Kaper (Univ. Amsterdam),
J. Sollerman (Univ. Stockholm), on behalf of the X-shooter GRB
collaboration, and 
A. Updike (Clemson Univ.), J. Greiner, T. Kruehler (MPE Garching),
on behalf of the GROND team, report:

We observed the optical afterglow of GRB 100621A (Ukwatta et al., GCN
10870; Updike et al., GCN 10874) with the ESO VLT equipped with the
X-shooter spectrograph. The afterglow was detected in the I-band
acquisition image. Four spectra lasting 10 minutes each were obtained,
covering the spectral range 3000-25000 AA, starting on 2010 June 21,
at 10:09 UT (7.1 hr after the GRB); the observations were done during
twilight. Preliminary inspection of the spectrum reveals emission
features which we interpret as due to [O II] 3727, Hbeta and the
[O III] doublet from the underlying host galaxy, at a common redshift
z = 0.542. The [O II] line is very weak. This, together with the low
redshift and the optically faint and red afterglow supports high
extinction internal to the host (Updike et al., GCN 10874).

We caution that the data reduction was carried out using archival
calibration files. We acknowledge a particularly helpful and attentive
support from the ESO staff in Paranal: M. Olivares, T. Rivinius,
C. Ledoux, C. Martayan, and the visiting astronomers: F. Ferraro,
B. Lanzoni.
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