TITLE:   GCN CIRCULAR
NUMBER:  30692
SUBJECT: GRB 210822A: NOT photometry and spectroscopy
DATE:    21/08/23 08:25:52 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

Z.P. Zhu (NAOC, HUST), L. Izzo (DARK/NBI), S.Y.Fu, D. Xu (NAOC), J.P.U. 
Fynbo (DAWN/NBI), E. Paraskeva, S. Vitali (NOT), report on behalf of a 
larger collaboration:

We observed the bright optical afterglow of GRB 210822A (Page et al., 
GCN 30677; Wang et al., GCN 30678; Ohno et al., GCN 30687) using the 
Nordic Optical Telescope (NOT) equipped with the ALFOSC camera.

We obtained 3x120s frames in the Sloan r-filter, starting at 23:11:50 UT 
on 2021-08-22 (i.e., ~ 13.89 hr after the BAT trigger). The previously 
reported optical afterglow (e.g., Page et al., GCN 30677; Zheng & 
Filippenko, GCN 30679; Butler et al., GCN 30680; Lipunov et al., GCN 
30681; Fu et al., GCN 30684) has decayed to m(r) = 19.71 +/- 0.02, 
calibrated with the PS1 field.

Subsequently 4x1200 s spectroscopy was carried out. A continuum is 
detected over the whole wavelength range of 3700-9500 AA, superimposed 
with some absorption features, among which prominent Fe II, Mg II, Mg I, 
and Al III lines were identified at a common redshift of z = 1.736. We 
conclude that this is the redshift of the burst.