GCN Circular 32141
Subject
GRB 220527A: NOT optical photometry and spectroscopic redshift
Event
Date
2022-05-28T06:34:21Z (4 years ago)
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.