GCN Circular 22996
Subject
GRB 180720B: VLT/X-shooter redshift
Date
2018-07-21T14:34:50Z (6 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
P. M. Vreeswijk (Radboud Univ. Nijmegen), D. A. Kann (HETH/IAA-CSIC), K.
E. Heintz (Univ. Iceland and DAWN/NBI), A. de Ugarte Postigo
(HETH-IAA/CSIC and DARK/NBI), B. Milvang-Jensen (DAWN/NBI), D. B.
Malesani (DARK/NBI and DAWN/NBI), S. Covino (INAF/Brera), A. J. Levan
(Univ. Warwick), G. Pugliese (Amsterdam), report on behalf of the
Stargate collaboration:
We observed the optical counterpart of GRB 180720B (Siegel et al., GCN
22973; Martone et al., GCN 22976) with the ESO VLT UT2 equipped with the
X-shooter spectrograph. Two spectra of 600 s each were secured starting
on 2018 July 21.384 UT (0.786 days after the GRB), covering the
wavelength range 3000-25000 AA.
A bright continuum is detected across the entire observed range. Several
absorption features are detected, which can be identified as due to Fe
II, Mg II, Mg I, and Ca II, all at z = 0.654. We also identify
fine-structure transitions due to both Fe II* and Ni II**, thus making
the redshift association with the GRB secure.
We acknowledge the ESO observing staff at Paranal, in particular Juan
Carlos Munoz, Emanuela Pompei, and Luca Sbordone.