[vsnet-grb-info 5943] GRB 080411: VLT redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7587
SUBJECT: GRB 080411: VLT redshift
DATE:    08/04/12 01:51:01 GMT
FROM:    Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center  <malesani at astro.ku.dk>

Christina C. Thoene (DARK/NBI), Annalisa De Cia (Univ. Iceland), Daniele 
Malesani, and Paul M. Vreeswijk (DARK/NBI), report:

We observed the optical afterglow of GRB 080411 (Marshall et al., GCN 
7584; Kruehler et al., GCN 7586) wih the ESO VLT equipped with FORS1 
with grism 300V. In a 600 s exposure taken at large airmass (average of 
2.45) the afterglow trace is clearly detected. The mean time of the 
observations is Apr 11.987 UT (2.4 hr after the trigger). In the 
acquisition image, we measure R = 17.25 based on archival zeropoints.

We detect very strong absorption lines from Mg II, Mg I, Fe II and 
several other ions at a redshift z = 1.03. Given the strength of the 
features, we consider this to be the redshift of the GRB. We caution 
that the wavelength calibration is based on archival data.

We acknowledge excellent support from the ESO staff, who carried out 
this difficult observation, in particular Swetlana Hubrig.