TITLE:   GCN CIRCULAR
NUMBER:  32141
SUBJECT: GRB 220527A: NOT optical photometry and spectroscopic redshift
DATE:    22/05/28 06:34:21 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

D. Xu (NAOC), Z.P. Zhu (NAOC, HUST), L. Izzo (DARK/NBI), S.Y. Fu, X. Liu 
(NAOC), M. Aron (NOT), report on behalf of a larger collaboration:

We observed the field of GRB 220527A detected by AGILE (Ursi et al., GCN 
32129), Fermi (Fermi GBM team, GCN 32130; Bissaldi et al., GCN 32131), 
CALET (Yamaoka et la., GCN 32139), and AstroSat (Gopalakrishnan et al., 
GCN 32140), using the 2.56-m Nordic Optical Telescope (NOT) equipped 
with the ALFSOC camera. We carried out 3x120 s Sloan r-band photometry 
starting at 03:55:22 UT on 2022-05-28, i.e., 18.6 hr since the Fermi/GBM 
trigger, followed by 2x1800 s spectroscopy covering wavelength of ~ 3600 
- 9000 AA.

The previously reported optical afterglow (Tohuvavohu et al., GCN 32136; 
Imai et al., GCN 32138) is clearly detected in each single r-band image, 
and has decayed to r = 19.55 +/- 0.02 mag, calibrated with the 
PAN-STARRS field.

A blue continuum is throughout the spectrum, superimposed with a few 
relatively prominent absorption features, among which we identify as Ni 
II, Fe II, Mn II, Mg II, all at a common redshift of z =0.857, using old 
calibrations. A weak emission feature might also be detected, 
interpreted as due to [O II] at the same redshift. We thus conclude z 
=0.857 is the redshift of the burst.