TITLE: GCN CIRCULAR NUMBER: 43876 SUBJECT: EP260227a: likely GTC/OSIRIS+ redshift z = 2.714 DATE: 26/02/28 12:12:32 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), R. A. J. Eyles-Ferris (Leicester), J. van Dalen (Radboud), D. Mata-Sanchez (IAC and ULL), A. de Ugarte Postigo (LAM), N. Castro Rodríguez (GTC), A. L. Cabrera Lavers (GTC) report on behalf of a larger collaboration: We observed the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris & Tanvir, GCN 43875) of EP260227a (Wang et al., GCN 43869) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ spectrograph. Our observations consisted of 4 exposures of 900 s each, using grism R1000B which covers the wavelength range 3670 - 7700 Å. The observation start time was 2026-02-28 at 03:16 UT (~7.1 hr after the trigger). In the acquisition magnitude, we measure r = 21.55 +/- 0.07 AB at mid time 6.89 hr after trigger (consistent with the NOT measurement; Fu et al., GCN 43873). This value is calibrated against nearby objects from the Pan-STARRS catalog and not corrected for Galactic extinction. A faint trace is detected down to ~4000 Å, with an apparent spectral break around 4500 Å which is interpreted as due to H I and the onset of the Lyman forest. A few weak, narrow features, due to Si II 1259, Si II 1304, C II 1334, C IV 1548/1550, allow us to measure a redshift z = 2.714. View this GCN Circular online at https://gcn.nasa.gov/circulars/43876. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...