GCN 43604: GRB 260131A/B: GTC/OSIRIS+ redshift confimation

R. Sanchez-Ramirez, A. J. Castro-Tirado, M.D. Caballero-Garcia, S. Guziy, S.-Y. Wu, I. Perez-Garcia, and E. Fernandez-Garcia (IAA-CSIC), D. Garcia-Alvarez (GTC), Y.-D. Hu (GXI), M. Gritsevich (Univ. of Helsinki), and L. Piro (INAF/IAPS), on behalf of a larger collaboration, report:


Following the detection of GRB 260131A/B (Fermi/GBM Team, GCN 43579; Sugai et al., GCN 43580; Roberts et al., GCN 43585; Frederiks et al., GCN 43590; Luo et al., GCN 43591), we observed the optical afterglow detected by several facilities (Gompertz et al., GCN 43586; Lee et al., GCN 43587; Saccardi et al., GCN 43595; García García et al., GCN 43599, Jiang et al. GCN 43600, Shi et al. GCN 43601), 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 data consisted of 3x900s exposures using grism R1000R, covering the spectral range between 5,000 and 10,000 A. The observations started on Feb 1 at 20:08 UT (i.e. ~37h after the burst trigger). From a preliminary reduction, we find the absorption system reported by Saccardi et al. (GCN 43595) at a consistent z=1.435. We note also the presence of FeII* lines.