TITLE:   GCN CIRCULAR
NUMBER:  41787
SUBJECT: GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
DATE:    25/09/11 09:25:59 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) and D. B. Malesani (DAWN/NBI and Radboud) report:

We carried out a full reduction of the spectrum of GRB 250404A / EP250404a observed with the GMG-2.4m telescope (Li et al., GCN 40084) using the most up-to-date calibrations and complete pipeline procedures.

A Ly-alpha absorption feature at ~4400 AA was reported by the Xinglong-2.16 m telescope (Zhu et al., GCN 40061).

In the GMG spectrum, the region around ~4400 AA exhibits a smooth continuum, and no typical Ly-alpha absorption feature is identified. However, we identified multiple metal absorption features, including Si IV at 1394 AA, Si IV at 1403 AA, Si II at 1527 AA, C IV at 1549 AA, Fe II at 1608 AA, Al II at 1671 AA, Al III at 1855 AA, Al III at 1863 AA, Zn II/Cr II at 2026 AA, Zn II/Cr II at 2062 AA, Fe II at 2344 AA, Fe II at 2374 AA, and Fe II at 2383 AA. These features consistently indicate a redshift of z = 1.88.

In summary, we conclude that the redshift of the transient is z = 1.88 (see Figure B1 of Yin et al., 2025; doi:10.3847/2041-8213/adf552).

We are grateful to D. B. Malesani for kindly pointing out the issue with the redshift determination.
 
We apologize for any confusion that our preliminary report may have caused.