TITLE: GCN CIRCULAR NUMBER: 45022 SUBJECT: EP260623a: OSIRIS+/GTC redshift z = 0.703 DATE: 26/06/23 05:47:48 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com> L. Izzo (INAF/OACN and DARK/NBI), A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud), S. Geier (GTC), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), G. Lombardi (GTC), A. Martin-Carrillo (UCD), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), F. Pérez Toledo (GTC) and A. Pérez (GTC) report: We observed the optical counterpart (Li et al. GCN 45021) of EP260623a (Wang et al, GCN 45020) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. In the 10-s acquisition image (beginning on 2026-06-23 at 04:44:12 UT, that is 1.83 hr after trigger), the optical afterglow is well detected with a magnitude 17.01 ± 0.05 (AB), calibrated against nearby LS objects, and not corrected for Galactic extinction. A total of 2 spectra of 600 s were secured, starting on 2026-06-23 at 04:49:58 UT (1.93 hr after EP trigger), using grism R1000B. Continuum is visible over the wavelength range 3615-7800 AA. A number of metal absorption features are detected, which we interpret as due to FeII, MnII, MgII, MgI, as well as multiple FeII fine structure transitions all at a common redshift z = 0.703, which we suggest to be the redshift of EP 260623a. This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). View this GCN Circular online at https://gcn.nasa.gov/circulars/45022. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...