TITLE:   GCN CIRCULAR
NUMBER:  38027
SUBJECT: GRB 241030A / EP241030a: GMG possible spectroscopic redshift at  z ~ 1.4
DATE:    24/11/01 09:10:37 GMT
FROM:    Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>

R.-Z. Li, H. Lin, S.-S. Li, H.-C. Feng, B.-T. Wang, F.-F. Song, J. Mao and J.-M. Bai (YNAO, CAS) report:

We observed the optical counterpart of GRB 241030A (Klingler et al., GCN 37956; Watson et al., GCN 37957; Fernández-Rodríguez et al., GCN 37958; Zheng et al., GCN 37959; An et al., GCN 37960; Higuchi et al., GCN 37963; Qiu et al., GCN 37965; Lin et al., GCN 37966; Wu et al., GCN 37970; Breeveld &amp; Klingler, GCN 37974; Méndez-Lapido et al., GCN 37993; Moskvitin et al., GCN 38016; Busmann et al., GCN 38019; Schneider et al., GCN 38021), which was independently detected by Fermi/GBM (Fermi GBM Team, GCN 37955), Swift (Klingler et al., GCN 37956), SVOM/GRM (SVOM/GRM Team, GCN 37972), and Einstein Probe (Wu et al., GCN 37997; Liang et al., GCN 38026) as EP241030a.

The observation was conducted with the Gao-Mei-Gu (GMG) 2.4m telescope. Grism #3 was used, providing a wavelength coverage of 3400–9100 AA. A single 1-hour spectrum was obtained, with exposure beginning at 13:15:33 UT on 2024-10-30, about 7.46 hours after the Swift trigger.

Despite the low signal-to-noise ratio of the spectrum, we identified a strong absorption line of Al II at 1671 AA, along with weaker absorption lines of Fe II at 2374 AA, 2383 AA, 2587 AA, and 2600 AA, Mg II at 2800 AA, and Mg I at 2852 AA. These metal absorption features consistently indicate a redshift of z ~ 1.4, consistent with the Keck/LRIS result (Zheng et al., GCN 37959).

We acknowledge the staff at the Lijiang Observatory for conducting the observation.