TITLE:   GCN CIRCULAR
NUMBER:  20321
SUBJECT: GRB 161219B: VLT/X-shooter redshift
DATE:    16/12/21 14:25:47 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>

N. R. Tanvir (U. Leicester), T. Kruehler (MPE), K. Wiersema (U. 
Leicester), D. Xu (NAOC/CAS), D. Malesani (DARK/NBI), B. Milvang-Jensen 
(DARK/NBI), and J. P. U. Fynbo (DARK/NBI) report on behalf of a larger 
collaboration:

We observed the optical counterpart of GRB 161219B (Swift trigger 
727541; D'Ai et al., GCN #20296) with the ESO Very Large Telescope UT 2 
(Kueyen) equipped with the X-shooter spectrograph, covering the 
wavelength range 3200-22000 AA. Observations started at 06:34 UT on 
2016-12-21, roughly 36 hr after the burst and consisted of 4 exposures 
of 600 s each. We measure r ~ 19.5 mag from the acquisition image.

Our spectrum exhibits absorption features from Mg II, Mg I, Ca H, Ca K, 
all at a common redshift of z = 0.1475. We also detect nebular lines 
from the Balmer series, [O II] and [O III] at a consistent redshift, 
which we conclude is the redshift of the GRB. The emission features are 
likely coming from the object visible in the PanSTARRS data, first 
noticed by Kruehler et al. (GCN 20299).

We acknowledge excellent support from the ESO observing staff in 
Paranal, in particular Julien Milli, Thomas Rivinius, and Dimitri Gadotti.