TITLE: GCN CIRCULAR NUMBER: 40061 SUBJECT: EP250404a: Xinglong-2.16m spectroscopic redshift DATE: 25/04/04 18:05:48 GMT FROM: Dong Xu at NAOC/CAS dxu@nao.cas.cn
Z.P. Zhu, J. An, X. Liu, S.Q. Jiang, J.J. Jin, Z. Fan, D. Xu (NAOC), S.Y. Fu (HUST), report on behalf of a large collaboration:
We carried out spectroscopy of the optical counterpart (e.g., Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058) of EP250404a (Hu et al., GCN 40051), likely the identical event to GRB 250404A (GBM team, GCN 40050), using the 2.16-m telescope equipped with the BFOSC instrument, located at Xinglong, Hebei, China. Our spectra cover the wavelength range 3800 - 9000 AA, and consist of 2 exposures of 1800 s each.
The continuum is throughout the spectrum. From the detection of a broad Lya absorption feature at ~ 4400 AA and relatively weak absorption features, which interpreted as being due to Si IV and Al III, we infer a common redshift of z = 2.63. We conclude this is the likely redshift of the event.
An intervening system is also detected with absorption features, interpreted as being due to Mg II and Fe II, we inferred its redshift of z = 1.88.
We acknowledge the expert support from the Xinglong-2.16m staff, in particular Junjun Jia and Jie Zheng.
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