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 ��. 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 Elizabeth Bartlett, Eleonora Sani, Steffen Mieske, and Jose
Velasquez, and the visiting astronomers Gerard Gilmore, Amelia Bayo, and
[GCN OPS NOTE(17nov16): Per author's request, the last paragraph was modified.]