GCN Circular 45605
Subject
GRB 260914A: 2.2m CAHA optical afterglow detection and 10.4m GTC redshift confirmation
Event
Date
2026-09-17T04:04:09Z (12 days ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
Via
email
A.J. Castro-Tirado (IAA-CSIC), Y.-D. Hu (GXU), I. Perez-Garcia, M.D. Caballero-Garcia, M. Gritsevich, S. Guziy (IAA-CSIC), J. F. Agui Fernandez, M.M. Sanchez Andujar (CAHA), D. Slumstrup and D. Perez-Valladares (IAC, GRANTECAN), on behalf of a larger collaboration, report:
Following the detection of GRB 260914A by SVOM/ECLAIRs (Wang et al. GCN 45562), we triggered the 2.2m CAHA telescope (equipped with CAFOS) in Almeria (Spain). Images in the Sloan g, r, i and z bands were gathered on Sep 14 starting at 22:01 UT (i.e. ~10.85 hours after the trigger).
We still detect the optical afterglow in the gri-bands, confirming the fast decay based in all reports published so far (Akl et al., GCN 45564; Palmerio et al., GCN 45565; Li et al., GCN 45566; Shi et al., GCN 45567, Saccardi et al., GCN 45568, Volnova et al., GCN 45595). On Sep 14, 22:28 UT, we measure i: 21.1 ± 0.1 (on a 600s image coadd).
We also obtained optical spectroscopy at the 10.4m GTC telescope (equipped with OSIRIS+) in La Palma (Spain) on Sep 15, starting at 04:27 UT (i.e. ~17.25 hours after the trigger), covering the range 3800-9500 A. Based on a preliminary analysis, we identify emission lines of [O II] and H-beta, thus confirming the redshift of the underlying star-forming galaxy at z ~0.778, as reported by Saccardi et al. (GCN 45579) and Yan et al. (GCN 45582).
Moreover, in the faint continuum extending to the bluest wavelengths in the R1000B grism (3x750s exposure), we tentatively identify the Mg II doublet in absorption at the redshift of z ~0.778, thus supporting other findings (Yan et al. GCN 45582) and confirming the association between GRB 260914A and the underlying above-mentioned galaxy.
We thank the staff at both CAHA and GTC for their excellent support.