GCN Circular 42053
Subject
GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162
Event
Date
2025-10-02T09:33:41Z (a month ago)
From
Ruben Sanchez-Ramirez at IAA-CSIC <ruben@iaa.es>
Via
Web form
R. Sanchez-Ramirez (IAA-CSIC), Y.-D. Hu (GXI), A. J. Castro-Tirado, S. Guziy, M.D. Caballero-Garcia, S.-Y. Wu and I. Perez-Garcia (IAA-CSIC), R. Scarpa (GTC, IAC), D. Gonzalez (GTC), A. Cabrera-Lavers (GTC, IAC), S. B. Pandey (ARIES), M. Gritsevich (Univ. of Helsinki), J. Becerra-Gonzalez (IAC), L. Piro (INAF/IAPS) and B.-B. Zhang (NJU), on behalf of a larger collaboration, report:
Following the detection of GRB 251001B by Fermi (Fermi Team, GCN 42038, Neights et al. GCN 42047) and Swift (Beardmore et al. GCN 42039), we observed the optical afterglow (Gompertz et al. GCN 42040, An et al. GCN 42041, Strausbaugh et al. GCN 42043, O'Neill et al. GCN 42046, de Ugarte Postigo et al., GCN 42050, Ma et al., GCN 42051) with the 10.4m GTC telescope, at the Spanish Roque de los Muchachos Observatory, on the island of La Palma, equipped with the OSIRIS+ instrument.
The spectroscopic observations were performed at high airmass and consisted of 3x900s exposures using grism R1000B, with a spectral coverage between 3,600 and 7,700 A (R~600). The observations started on Oct 2, 02:39 UT (i.e. 12.35 h after the burst trigger).
From a preliminary reduction, we find a strong DLA at ~4000A, as well as several metal absorption lines that we interpret as coming from NV, SiII, SiII*, OI, CII, SiIV, CIV, FeII, FeII*, AlII, AlIII, ZnII, CrII, all at z=2.162. The detection of SiII* and FeII* links this system to the GRB. We also note the presence of Lya in emission at the same redshift.