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GCN Circular 32647

Subject
GRB 221009A: Nanshan/NEXT photometry and Xinglong-2.16m spectroscopy
Date
2022-10-10T09:19:26Z (2 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
D. Xu, S.Q. Jiang, S.Y. Fu, X. Liu (NAOC), Z.P. Zhu (NAOC, HUST), T.H. 
Lu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:

We observed the field of the optical counterpart of Swift J1913.1+1946 
or GRB 221009A detected by Swift (Dichiara, GCN 32632), using the 
NEXT-0.6m telescope located at Nanshan, Xinjiang, China. Observations 
started at 14:25:55 UT on 2022-10-09, i.e., 762 s after the Swift/BAT 
trigger. A series of frames in the Sloan r- and z- filters were obtained.

The optical counterpart is clearly detected in each of our images, which 
decays from r ~ 14.93 to r ~ 16.50 within ~ four hours, with a decay 
index of \alpha ~ 0.5 (F_t ~ t^-\alpha), calibrated the nearby PS1 
stars. The decaying behavior is consistent with that for conventional 
GRBs.

Spectroscopy of the optical counterpart was performed at the 2.16m 
telescope equipped with the BFOSC camera at Xinglong, Hebei, China. The 
spectrum covers the wavelength range 3800-9000 AA. The observation mid 
time is 2022 Oct 10.63 UT, i.e., 0.95 hr after the BAT trigger.

The spectrum is dominated by a red continuum due to very high Galactic 
extinction, and no prominent absorption feature can be identified. Given 
the detections by Swift/UVOT as well as spectral continuum, the event 
could be real GRB 221009A at a rather low redshift.

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