TITLE: GCN CIRCULAR NUMBER: 43595 SUBJECT: GRB 260131A: NOT spectroscopic redshift z = 1.434 DATE: 26/02/01 22:04:19 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk> A. Saccardi (CEA/Irfu), J. An (NAOC), G. Corcoran (UCD), B. Gompertz (Birmingham), L. Izzo (INAF/OAC and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), B. Schneider (LAM), A de Ugarte Postigo (LAM), K. Valeckas (NOT and NBI), report on behalf of a larger collaboration: We observed the optical counterpart GOTO26akj / AT2026bwg (Gompertz et al., GCN 43586; Lee et al., GCN 43587) of the Fermi and MAXI GRB 260131A (Roberts, GCN 43585; a.k.a. GRB 260131B: Sugai et al., GCN 43580) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC spectrograph. We measure the afterglow brightness to be r = 18.98 +/- 0.02 (AB) at a mean epoch 2026 Feb 01 at 19:45:24 UT (37.1 hr after the burst), calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction. A spectrum consisting of 4x900 s exposures was secured starting on 2026 Feb 01 at 19:57 UT (37.3 hr after the Fermi/GBM trigger), using grism #4 which covers the wavelength range 3200-9600 AA. Based on a preliminary reduction of part of the spectra, a continuum is detected down to 3600 AA, setting an upper limit to the redshift z < 1.95 based on the lack of HI absorption. From the detection of several absorption features, among which Mg II 2804/2796, Fe II 2600, Fe II 2382, and Al III 1863/1855, we infer a redshift z = 1.434. Further analysis is ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/43595. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...