TITLE: GCN CIRCULAR NUMBER: 42227 SUBJECT: GRB 251013C: NOT spectroscopic redshift z = 0.572 DATE: 25/10/13 21:02:05 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie> A. Martin-Carrillo (UCD), L. Izzo (INAF/OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), B. Schneider (LAM), A. de Ugarte Postigo (LAM), A. Saccardi (CEA/Irfu), B. P. Gompertz (Birmingham), K. Valeckas (NOT and NBI) report on behalf of a larger collaboration: We observed the optical afterglow (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226) of GRB 251013C (Rakotondrainibe et al., GCN 42222; Fermi GBM team, GCN 42221) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A spectrum using grism #4 was secured starting on 2025-10-13 at 19:46:24 UT (2.11 hr after the GRB), under good conditions. The exposure time was 2x1200 s and the covered wavelength range is 3500-9600 AA. In a preliminary reduction of the spectra, we clearly detect a continuum over the whole covered wavelength range. From the detection of multiple absorption features, including Fe II 2600, the Mg II doublet, weak Mg I, and the Ca II doublet, we infer a redshift of z = 0.572. Photometry of the afterglow was carried out in the ugriz filters. In a 30-s r-band image, we measure r = 16.52 +/- 0.02 AB (at a time of 2.88 hr after the GRB), calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42227. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...