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GCN Circular 31353

GRB 220101A: Xinglong-2.16m photometry and spectroscopy
2022-01-01T15:51:07Z (2 years ago)
Dong Xu at NAOC/CAS <>
S.Y. Fu (NAOC), Z.P. Zhu (NAOC, HUST), D. Xu, X. Liu, S.Q. Jiang (NAOC) 
report on behalf of a larger collaboration:

We observed the field of GRB 220101A detected by Swift (Tohuvavohu et 
al., GCN 31347) and Fermi (Arimoto et al., GCN 31350) using the 
Xinglong-2.16m telescope equipped with the BFOSC camera. Observations 
were carried out starting at 09:50:07 UT on 2022-01-01. We firstly 
obtained 4x300 s frames in each of the B, V, R and I bands, and then 
2x1800 s spectroscopy covering ~3800 - 8800 AA.

The optical afterglow of the burst (Tohuvavohu et al., GCN 31347) is 
clearly detected in each of our stacked images in the V, R and I bands, 
but no in the B band. Preliminary photometry is as follows:

Tmid-T0 (hr)   Mag     MagErr  Filter
   5.55           >21.43       N/A      B
   5.45            19.86        0.06      V
   5.36            18.65        0.02      R
   5.27            17.34        0.01      I

The spectrum is in low resolution and rather low S/N. However, a broad 
absorption feature is evident centering at ~ 6820 AA, which can 
interpreted as Ly_alpha absorption. Besides Ly_alpha, other weak lines 
such as Si II, C II, Si IV are also detected at the common redshift of z 
= 4.61. We thus conclude that z = 4.61 is likely the redshift of the GRB.

We thank the great support of the Xinglong-2.16m staff, in particular 
Junjun Jia, Yinan Zhu, Aiying Zhou, and Jie Zheng.
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