GCN Circular 44565
Subject
GRB 260511B: OSIRIS+/GTC redshift z=2.006
Event
Date
2026-05-11T23:06:28Z (5 months ago)
From
Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>
Via
email
A. de Ugarte Postigo (LAM), C. C. Thoene (AbAO), A. Martin-Carrillo (UCD), S. Geier (GTC), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), L. Izzo (INAF/OACN and DARK/NBI), G. Lombardi (GTC), D. B. Malesani (DAWN/NBI and Radboud), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), A. M. García Rodríguez (GTC) and D. González González (GTC) report:
We observed the optical counterpart (Wu et al. GCN 44547; Sasada et al. GCN 44549; Jiang et al. GCN 4455; Wu et al. GCN 44552; Waratkar et al. GCN 44556; Li et al. GCN 44557; Vijaykumar et al. GCN 44561) of GRB 260511B (Fermi GBM team GCN 44542; Godet et al. GCN 44543; Roberts et al. GCN 44554; Arya et al. GCN 44560) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument.
In the 30-s acquisition image (beginning on 2026-05-11 at 21:05:13.010 UT, that is 10.08 hr after trigger), the optical afterglow is well detected with a preliminary magnitude of r = 19.30 ± 0.05 (AB), calibrated against nearby SDSS objects, and not corrected for Galactic extinction.
A total of 3 spectra of 900 s were secured, starting on 2026-05-11 at 21:11:43.011
UT (10.19 hr after trigger), using grism R1000B. Continuum is visible over the complete wavelength range 3620-7800 AA. A trough is detected at the blue edge of the spectrum at ~3650 AA, which we identify as a DLA. A number of strong metal absorption features are detected, which we interpret as due to SII, SiII, SiII*, OI, CII, SiIV, CIV, FeII, FeII* AlII, NiII, NiII*, AlIII, CrII, ZnII, and MnII all at a common redshift of 2.006 +/- 0.001, which we suggest to be the redshift of GRB 260511B. Multiple intervening systems are also detected in the spectrum, including a strong system at z = 1.437 with lines due to SiII, CIV, FeII, AlII, AlIII, MgII.
This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774).