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GCN Circular 6952

Subject
GRB 071020: VLT spectroscopy
Date
2007-10-20T13:40:12Z (17 years ago)
From
Pall Jakobsson at U Hertfordshire <P.Jakobsson@herts.ac.uk>
Pall Jakobsson (U. Hertfordshire), Paul M. Vreeswijk,
Jens Hjorth, Daniele Malesani, Johan P.U. Fynbo and 
Christina C. Thoene (DARK, NBI) report:

Using FORS2 on the Very Large Telescope, we have obtained 
a 10 min spectrum (grism 300V) of the optical afterglow 
(OA) of GRB 071020 (Holland et al., GCN 6949). The acquisition 
image shows the proposed OA (Schaefer et al., GCN 6948) to 
have R ~ 20.4 on Oct 20.377 (2.0 hours post burst).

The spectrum displays Fe II (2586,2600) and the Mg II 
doublet (2796,2803) in absorption corresponding to a redshift 
of z = 2.145 (based on a preliminary wavelength calibration). 
Hence, the GRB is unrelated to the nearby z = 0.0166 galaxy
reported by Yuan et al. (GCN 6951).

We note that this is a lower limit to the GRB redshift.
There is some indication of a flux drop in the OA spectrum
around 4300 A, implying that the GRB redshift could be 
z ~ 2.5 if due to the Ly-alpha break.

We thank the Paranal staff for excellent support, 
especially Emanuela Pompei.
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