TITLE:   GCN CIRCULAR
NUMBER:  30164
SUBJECT: GRB 210610A: Xinglong-2.16m redshift
DATE:    21/06/10 17:26:59 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

Z.P. Zhu, D. Xu, S.Y. Fu, X. Liu (NAOC) report on behalf of a larger 
collaboration:

Following the photometry of the optical afterglow (Xu et al., GCN 30162) 
of GRB 210610A (Page et al., GCN 30160), we carried out 2x1800 s 
spectroscopy of the afterglow using the BFOSC camera. The spectrum 
covers the wavelength range 4000-9000 AA. The observation mid time is 
2021 June 10.667 UT, i.e., 0.955 hr after the burst.

In our spectra, continuum is detected over the whole observed range. A 
prominent absorption feature is detected around 5519 AA, which we 
identify as Ly alpha in absorption, and blueward of which is Ly alpha 
forest. The interpretation is confirmed by the detection of metal 
absorption lines such as Si II, Si IV, C IV, all at a common redshift z 
= 3.54, using old calibrations. The redshift measurement may be improved 
a bit when new calibrations are available.

We thank the excellent support of the Xinglong-2.16m staff, especially 
Junjun Jia and Jie Zheng.