{
  "body": "R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) report:\n\nGRB 250404A / EP250404a was detected by Fermi GBM (Fermi GBM team, GCN 40050) and by EP/WXT (Hu et al., GCN 40051). We observed the optical counterpart of GRB 250404A / EP250404a (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083). \n\nThe spectroscopic observation was conducted using the GMG-2.4m telescope with Grism #14, which provides a wavelength coverage of 3600–7460 AA. A single 1800s spectrum was obtained, with exposure beginning at 2025-04-04T15:18:24, about 0.98 hours after the Fermi/GBM and EP/WXT trigger (Fermi GBM team, GCN 40050; Hu et al., GCN 40051).\n\nTwo absorption systems were identified in the spectrum. \n\nFor the first absorption system, we detected multiple metal absorption features, including Si II at 1527 AA, Al II at 1671 AA, Al III at 1855 AA and 1863 AA, Zn II/Cr II at 2026 AA and 2062 AA, and Fe II at 2344 AA, 2374 AA, and 2383 AA. These features consistently indicate a redshift of z ~ 1.881. \n\nFor the second absorption system, the spectrum shows multiple metal absorption lines from Si II/S II at 1260 AA, O I/Si II at 1303 AA, C II at 1335 AA, Si IV at 1394 AA, Si II at 1527 AA, Fe II at 1608 AA, and Al III at 1863 AA. These absorption features correspond to a redshift of z ~ 2.627. \n\nThese results support a redshift of z ~ 2.627 for the transient, consistent with the measurement reported by Xinglong-2.16m (Zhu et al., GCN 40061).\n\nWe thank the staff at the Lijiang Observatory for their support in conducting the observation.",
  "createdOn": 1743911838383,
  "bibcode": "2025GCN.40084....1L",
  "circularId": 40084,
  "eventId": "GRB 250404A",
  "submitter": "Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>",
  "format": "text/plain",
  "subject": "GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627",
  "submittedHow": "web"
}