TITLE:   GCN CIRCULAR
NUMBER:  44656
SUBJECT: GRB 260516D: GTC/OSIRIS+ spectroscopic redshift z = 1.801
DATE:    26/05/17 04:17:13 GMT
FROM:    Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>

L. Izzo (INAF/OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), A. de Ugarte Postigo (LAM), S. Geier (GTC), A. Martin-Carrillo (UCD), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), F. Perez Toledo (GTC) report:

We observed the optical counterpart (Li et al., GCN 44654; Mohan et al., GCN 44655) of GRB 260516D (Brunet et al., GCN 44649) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument.

In the 30-s acquisition image (beginning on 2026-05-17 at 02:54:51, that is 6.25 hr after trigger), the optical afterglow is well detected with a magnitude 21.0 ± 0.1 (AB), calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction.

A total of 3 spectra of 900 s were secured, starting at 03:06:24.010 UT (6.44 hr after trigger), using grism R1000B. Continuum is visible over the range 3650-7800 AA. A number of metal absorption features are detected, which we interpret as due to, among others, C II, C IV, Si II, Fe II, Al II, and Al III, all at a common redshift z = 1.801, which we suggest to be the redshift of GRB 260516D.

This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774).