[vsnet-grb-info 6329] GRB 080707: VLT redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7949
SUBJECT: GRB 080707: VLT redshift
DATE:    08/07/07 12:42:24 GMT
FROM:    Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center  <malesani at astro.ku.dk>

Johan P. U. Fynbo, Daniele Malesani, & Bo Milang-Jensen (DARK), report 
on behalf of a larger collaboration:

We observed the field of GRB 080707 (Schady et al., GCN 7947) with the 
ESO VLT equipped with FORS1.

Inside the XRT error circle, we detect the object first reported by 
Clemens et al. (GCN 7984) in the R and I bands. The source had R ~ 19.6 
on 2008 Jul 7.385 UT (47 min after the trigger), calibrated against 
USNO-B1. This object is not visible in the DSS (which reaches a deeper 
limit) and seems brighter than in the later observation reported by 
Clemens et al. (GCN 7984). It is thus very likely the optical afterglow 
of GRB 080707. A finding chart is posted at

http://www.astro.ku.dk/~malesani/GRB/080707/080707_finder.jpg

FORS1 spectra were acquired between Jul 7.397 and 7.441 UT with grism 
300V. From detection of FeII and MgII absorption features, we infer a 
redshift z = 1.23. A conservative upper limit z < 2.2 can be set from 
the lack of Lyman alpha forest in the blue

We acknowledge excellent and enthusiastic support from the observing 
staff at Paranal, in particular Chris Lidman, Lorena Faundez, Claudia 
Reyes, and Dominique Naef.