TITLE:   GCN CIRCULAR
NUMBER:  38814
SUBJECT: GRB 250103A: NOT spectroscopic redshift
DATE:    25/01/04 03:37:11 GMT
FROM:    Zipei Zhu at NAOC <zpzhu@nao.cas.cn>

Z.P. Zhu, D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Saccardi (CEA/Irfu), K. Valeckas (NBI) report on behalf of a large collaboration:

We carried out spectroscopy of the optical counterpart (e.g., Li et al., GCN 38795; Qiu et al., GCN 38802; Xu et al., GCN 38808; Leonini et al., GCN 38811) of GRB 250103A detected by SVOM/ECLAIRs (Wang et al., GCN 38786) and Fermi/GBM (Trigg et al., GCN 38806), using the the ALFOSC instruments mounted on the Nordic Optical Telescope (NOT). Observations started at 21:49:26 UT on 2025-01-04, i.e., 11.88 hrs after the burst, consisted of 2 exposures of 1200 s each, and the spectra cover the wavelength range 3600 - 9000 AA.

The whole spectrum has a fairly low S/N, but absorption features are evident. From the detection of a Lya absorption feature at ~ 6088 AA and multiple absorption features, which interpreted as being due to Si II, C II, Si IV, C IV, Fe II, and Al II, we infer a common redshift of z = 4.01, fully consistent with the measurement from GTC (de Ugarte Postigo et al., GCN 38809). We conclude this is the redshift of the burst.