GCN Circular 41952
Subject
GRB 250920C: SALT redshift confirmation
Event
Date
2025-09-23T12:27:05Z (2 days ago)
From
Simon de Wet at DTU Space <simdewet@gmail.com>
Via
Web form
S. de Wet (DTU Space), D. A. H. Buckley (SAAO), D. B. Malesani (DAWN/NBI and Radboud), P. J. Groot (Radboud, UCT, and SAAO) report:
We observed the optical afterglow (Wortley et al., GCN 41907) of GRB 250920C (Gupta et al., GCN 41904), using the Southern African Large Telescope (SALT) equipped with the Robert Stobie Spectrograph (RSS). Observations started at 23:11:13 UT on 2025 Sep 20 (7.8 hr after the GRB), and consisted of 2x1200 s of spectroscopy using the PG700 grating (which covers the wavelength range 3600-7500 AA).
In the coadded spectrum, continuum is detected across the whole wavelength range. A few narrow absorption features are visible which we interpret as due to C IV 1548,1550 (very strong), Fe II 2344 and 2374, Mg II 2796,2803 and Mg I 2852, all at a redshift of 1.399. Our result is thus consistent with, and confirms, the earlier measurement reported by Sanchez-Ramirez et al. (GCN 41928) using the GTC.