[vsnet-grb-info 19952] GRB 171020A: NOT spectroscopic redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22039
SUBJECT: GRB 171020A: NOT spectroscopic redshift
DATE:    17/10/21 16:43:25 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

D. Malesani (DARK/NBI), J. P. U. Fynbo (NBI), K. E. Heintz (Univ. 
Iceland and DARK/NBI), M. Stone (Turku Univ.), K. Karhunen (Turku 
Univ.), report on behalf of a larger collaboration:

Following our imaging sequence (Malesani et al., GCN 22029), we secured 
spectra of the optical afterglow of GRB 171020A (Page et al., GCN 
22028), using the AlFOSC spectrograph at the Nordic Optical Telescope. A 
total of 4x1200 s exposure was secured using grism #4, covering the 
wavelength range ~3600-9400 AA. Spectroscopy started on 2017 Oct 21.005 
UT (1 hr after the trigger).

A faint trace is detected down to at least ~4000 A. Several weak 
absorption features are detected, which we interpret as due to Mg II, Fe 
II, and C IV all at a common redshift z = 1.87.

We thank the NOT staff for support, in particular Amanda Djupvik and 
Sergio Armas.