GCN Circular 30583
D.A. Kann (HETH/IAA-CSIC), L. Izzo (DARK/NBI), A.J. Levan (Radboud), D.B. Malesani (DTU Space), S. de Wet (UCT) report for the STARGATE collaboration: "We observed the afterglow of GRB 210731A (Troja et al. GCN 30568, de Wet et al. GCN 30570) with the ESO VLT UT3 equipped with the X-shooter spectrograph on 1 Aug 2021. A total of 4800 s (4x1200 s) of spectra were obtained starting at 02:45 UT (approximately 28.5 hours after the burst). The afterglow is well detected in the acquisition imaging with r=20.7+/- 0.1, and a continuum is visible across the X-shooter spectral range. The spectra contain several prominent absorption features of Fe II, Al III, Mg II and Mg I, at a common redshift z=1.2525. This is consistent with the detection of the afterglow in all the UVOT filters (Kuin & Troja GCN 30572), and we suggest it to be the redshift of GRB 210731A. We thank the Paranal staff for the excellent assistance in securing these observations."