[AAVSO-HEN] GRB 080913: VLT/FORS spectrum

[grb at aavso.org]

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TITLE:   GCN CIRCULAR
NUMBER:  8225
SUBJECT: GRB 080913: VLT/FORS spectrum
DATE:    08/09/13 17:28:26 GMT
FROM:    Jochen Greiner at MPI  <jcg at mpe.mpg.de>

J.P.U. Fynbo (DARK/NBI), J. Greiner, T. Kruehler (both MPE),
A. Rossi (Tautenburg Obs), P. Vreeswijk, D. Malesani (both DARK/NBI)
report on behalf of a larger collaboration

Based on the rapid determination of an i'-band drop out we triggered 
VLT/ToO observations (program-ID 081.A-0135; PI Greiner) and obtained 
spectroscopy with FORS2+Gris600z of the afterglow of GRB080913
(Schady et al. 2008, GCN #8217; Stamatikos et al. 2008, GCN #8222). 
Observations started at 8:30, about 100 min after the GRB, and continued
until morning twilight. We detect a red continuum that disappears
bluewards of a break around 9400 AA. Interpreting this break
as the onset of the Lyman-alpha forest we infer a redshift
of about z=6.7 consistent with the photometric redshift determined
by GROND  (Greiner et al., GCN #8223).

We are very grateful for the excellent support by the Paranal
observatory staff, in particular Rachel Gilmour and Heidi Schmidt.