TITLE:   GCN CIRCULAR
NUMBER:  16902
SUBJECT: GRB141004A: Host galaxy redshift form GTC
DATE:    14/10/07 10:39:48 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte@iaa.es>

A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), C.C. Thoene (IAA-CSIC), 
D. Malesani (DARK/NBI), S. Schulze (PUC, MAS), R. Sanchez-Ramirez 
(UPV/EHU, IAA-CSIC), J. Gorosabel (UPV/EHU, IAA-CSIC),
C.A. Alvarez Iglesias (GTC, IAC), J. Molgo (GTC), and M. Rivero (GTC) 
report on behalf of a larger collaboration:

We obtained spectroscopy of the optical counterpart of GRB 141004A 
(D'Elia et al., GCN 16878, Mereghetti et al., GCN 16879) with OSIRIS at 
the 10.4m GTC telescope on October 7, starting at 5:10 UT (~30 hr after 
the GRB). In a preliminary reduction of a 2x600 s exposure with the 
R1000R grism (covering from 5100 to 10000 A with a resolution of ~1000), 
we detected several emission lines corresponding to [O II], H-beta and 
[O III] at a common redshift of 0.573. This confirms that the tentative 
emission line detection reported by Schulze et al. (GCN 16891) was 
indeed real and that it corresponds to the [O II] 3727/3729 doublet. 

We also detect emission from another galaxy within the slit at a similar 
redshift of 0.571, with a projected distance of 22" to the East, which 
corresponds to ~150 kpc at that redshift, probably belonging to the same 
galaxy group. The nearby galaxy reported by D'Elia et al. (GCN 16881) 
shows multiple emission features at a redshift of 0.279, and it is therefore 
unrelated to the GRB.