GCN Circular 19710

A. J. Castro-Tirado (IAA-CSIC), A. F. Valeev (SAO-RAS), S. Jeong (SKKU), 
R. S��nchez-Ram��rez (IAA-CSIC), V. V. Sokolov (SAO-RAS), P. Ferrero 
(IAA-CSIC), J. C. Tello (IAA-CSIC), Y. Hu (IAA-CSIC), B.-B. Zhang 
(IAA-CSIC), A. Pozanenko (IKI-RAS), S. R. Oates (U. of Warwick), S. 
Geier (GTC) and G. Lombardi (GTC), on behalf of a larger collaboration, 
report:

Following the detection of GRB 160623A by Fermi (Vianello et al. GCNC 
19553) and Konus-Wind (Frederiks et al. GCNC 19554), we observed the 
optical afterglow of GRB 160623A (Pozanenko et al. GCNC 19561) with the 
10.4m Gran Telescopio Canarias (GTC), gathering spectra at different 
epochs: June 25 (1.9 days post-burst) and July 3/4, with both the R1000B 
and R2500I grisms covering the range 3800-10000 A. At the position of 
the afterglow, the reddest spectrum (2 x 1200s with R2500I) showed 
H-alpha and [SII] in emission, from which we determine a redshift z = 
0.367, confirming the value proposed by Malesani et al. (GCNC 19708). 
The bluest range spectrum (1200s) also revealed a marginal detection of 
H-beta (taking into account the high foreground Galactic extinction in 
the line of sight). The faint continuum on the first epoch spectrum 
extended down to 3800 A with no absorption lines being present. 
Therefore we propose this is the redshift of the GRB 160623A host 
galaxy.

We acknowledge excellent support from the GTC staff.