TITLE:   GCN CIRCULAR
NUMBER:  21209
SUBJECT: GRB 170531B: WHT spectroscopy
DATE:    17/06/07 09:17:35 GMT
FROM:    Klaas Wiersema at U Leicester  <kw113@leicester.ac.uk>

K. Wiersema, N. Tanvir (Leicester), A. Levan (Warwick) report:

We observed the afterglow of GRB 170531B (Evans et al. GCN 21171; Lipunov et al. GCN 21173; 
Pozanenko et al. GCN 21174) with the 4.2m William Herschel Telescope on La Palma, using the 
ACAM instrument. We obtained a spectrum, consisting of 4x900 seconds exposure time, starting 
at 02:55 UT on 1 June 2017. Our wavelength coverage is ~4500 - 9500 A. We detect a small 
number  metal lines (at low S/N) at a redshift consistent with that obtained by de Ugarte-Postigo 
et al. (GCN 21177).

We warmly thank the staff of ING, in particular Raine Karjalainen, for their assistance.