[vsnet-grb-info 18325] GRB 160804A: VLT/X-shooter redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19773
SUBJECT: GRB 160804A: VLT/X-shooter redshift
DATE:    16/08/05 08:05:36 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu at nao.cas.cn>

D. Xu (NAOC), K. E. Heintz (DARK/NBI), D. Malesani (DARK/NBI and DTU 
Space), K. Wiersema (U. Leicester), J. P. U. Fynbo (DARK/NBI), report on 
behalf of a larger collaboration:

We observed the optical afterglow of GRB 160804A (Marshall et al., GCN 
19761; Breeveld et al., GCN 19764) with the ESO VLT UT2 (Kueyen) 
equipped with the X-shooter spectrograph. Observations started at 23:55 
UT on 2016-08-04 (22.37 hr after the BAT trigger) and consisted of 4 
spectra by 600 s each, covering the wavelength range 3500-20000 AA.

The continuum trace is well detected in our exposures, down to ~3100 AA.
The lack of any drop sets an upper limit to the redshift z < 1.55. A 
number of superimposed absorption features are detected, which we 
interpret as due to Mg I, Mg II, Fe II, Al II, as well as emission 
features due to [O II], [O III], Halpha, Hbeta, Hgamma, [N II], [S II], 
[S III], all at a common redshift z = 0.736. We thus conclude this is 
the redshift of GRB 160804A.

We acknowledge excellent support from the ESO observing staff in 
Paranal, in particular Jonathan Smoker, Leo Rivas, and Stephane Brillant.