[vsnet-grb-info 5191] GRB 071010B: Gemini Spectroscopic Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6888
SUBJECT: GRB 071010B: Gemini Spectroscopic Observations
DATE:    07/10/11 17:52:12 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko at srl.caltech.edu>

S. B. Cenko (Caltech), A. Cucchiara, D. B. Fox (Penn State), E. Berger
(Princeton), and P. A. Price (Hawaii) report on behalf of a larger
collaboration:

We have obtained a single 1800 s spectrum of the optical afterglow
(Oksanen; GCN 6873) of GRB071010B (Markwardt et al.; GCN 6871) with the
Gemini Multi-Object Spectrograph mounted on the Gemini North telescope.
Our exposure began at 14:41 UT on October 11, and covered the wavelength
range from 4000 - 8000 A.

We find a strong absorption doublet at ~ 5450 A that we identify as Mg II
2796 / 2803 at z = 0.947.  Weaker absorption features corresponding to Mg
I 2852 and Fe II 2586 are also present at the same redshift.  A
preliminary inspection reveals no other absorption nor emission systems
present.

If the z=0.947 system is the host redshift, we calculate an isotropic
energy release of ~ 1.1e52 erg in the 20 keV - 1 MeV observed frame
(Golenetskii et al., GCN 6879).