GCN Circular 44629
Subject
GRB 260515A: GTC/OSIRIS+ spectroscopic redshift z = 0.764
Event
Date
2026-05-16T01:11:21Z (15 days ago)
Edited On
2026-05-17T22:40:30Z (13 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
D. B. Malesani (DAWN/NBI and Radboud), S. Geier (GTC), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), L. Izzo (INAF/OACN and DARK/NBI), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), I. V. Yanes-Rizo (IAC), D. Pérez Valladares (GTC), F. Pérez Toledo (GTC) report:
We observed the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628) of GRB 260515A (Brunet et al., GCN 44622) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument.
In the 20-s acquisition image (beginning on 2026-05-15 at 23:48:49.010 UT, that is 4.67 hr after trigger), the optical afterglow is well detected with a magnitude r = 21.15 ± 0.10 (AB), calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction.
A total of 3 spectra of 1200 s were secured, starting on 2026-05-15 at 23:52:26.010 UT (4.73 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 Fe II, Mg II, and Mg I, all at a common redshift z = 0.764, which we suggest to be the redshift of GRB 260515A. We also detect emission due to the [O II] doublet at the same redshift.
This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774).