GCN Circular 6984
Subject
GRB 071020: BTA spectroscopy
Date
2007-10-24T15:00:41Z (17 years ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
T. A. Fatkhullin, V. V. Sokolov (SAO-RAS Nizhnij Arkhyz), S. Guziy
(Nikolaev St. Univ.), A. de Ugarte Postigo (ESO Santiago), D.
P�rez-Ram�rez (Univ. de Ja�n and U. Leicester), J. Gorosabel, M. Jel�nek
and A. J. Castro-Tirado (IAA-CSIC Granada), on behalf of a larger
collaboration, report:
"Following the detection of GRB 071020 by SWIFT (Holland et al. GCN
Circ. 6949) we obtained optical spectroscopy with the 6.0m BTA
telescope (+SCORPIO) of the SAO-RAS. In spite of poor weather
conditions (dense cirrus) we managed to get 4 x 1200s spectra of the
proposed optical afterglow (Schaefer et al. GCN Circ. 6948). The data
were taken on Oct 21.05 U.T. (i.e. 18 hr after the event), with the VPHG
400 grism (range 3700-9000 A).
We identify absorption lines from Fe II (2344, 2586 and 2600) and
possibly C IV (1548-1550) and Fe II (1608), at z = 2.142 � 0.002. This
confirms the lower limit to the GRB 071020 redshift derived from VLT
spectroscopy (Jakobsson et al., GCN Circ. 6952). Moreover, we do not
see any flux drop in the OA spectrum around 4300 A as the VLT spectrum
may suggest. However, there are indications of a flux drop at ~3870A but
the low S/N ratio in this range prevents us to draw any further
conclusion."
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