GCN Circular 42540
Subject
GRB 251103A: NOT spectroscopic redshift z = 0.76
Event
Date
2025-11-03T06:51:49Z (19 days ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
L. Izzo (INAF/OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), A. Saccardi (CEA/Irfu), A. de Ugarte Postigo (LAM), D. Xu (NAOC), S. Bijavara Seshashayana (NOT and Malmo Univ.), report on behalf of a larger collaboration:
We observed the optical afterglow (Schneider et al., GCN 42535; Turpin et al., GCN 42538; Gritsevich et al., GCN 42539) of GRB 251103A (Hu et al., GCN 42534; Fermi GBM team, GCN 42536) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A spectrum using grism #4 was secured starting on 2025 Nov 3.241 UT (61 min after the GRB), under good observing conditions. A total of 4 spectra of 600 s each were obtained, covering the wavelength range 3500-9600 AA.
In a preliminary reduction of the first spectrum, we detect a bright trace over the whole observed wavelength range. From the detection of multiple absorption features, including Fe II, Mg II, Mg I, and Ca II, we infer a redshift of z = 0.76.