[vsnet-grb-info 18731] GRB 161117A: VLT/X-shooter spectroscopy and redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20180
SUBJECT: GRB 161117A: VLT/X-shooter spectroscopy and redshift
DATE:    16/11/17 08:32:11 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

Daniele Malesani (DARK/NBI and DTU Space), Thomas Kruehler (MPE), Kasper 
E. Heintz (Univ. Iceland and DARK/NBI), and Johan P. U. Fynbo (DARK/NBI) 
report on behalf of a larger collaboration:

We observed the optical afterglow of GRB 161117A (Cummings et al., GCN 
20179) with the ESO VLT Kueyen equipped with the X-shooter spectrograph. 
In the acquisition image, taken on 2016 Nov 17.097 UT (0.73 hr after the 
GRB), the optical afterglow is clearly detected with a magnitude R ~ 19 
(assuming R = 18.10 for the USNO star at RA = 21:28:14.70, Dec = 
-29:37:08.8). The seeing was very poor, around 2.5", and the sky 
conditions were partially cloudy.

Four spectra by 600 s each were collected covering the full X-shooter 
wavelength range 3000-25,000 AA. A faint trace is detected, down to at 
least 3800 Å. Superimposed on it, we are able to identify a number of 
absorption features which we interpret as due to Mg I, Mg II, and Fe II, 
all at a common redshift z = 1.549.

We acknowledge excellent support from the ESO observing staff in 
Paranal, in particular Elisabeth Barlett, Eleonora Sani, Steffen Mieske, 
and Jose Velasquez.