TITLE:   GCN CIRCULAR
NUMBER:  46264
SUBJECT: GRB 261113A: 10.4m GTC spectroscopic confirmation of z = 3.58
DATE:    26/11/14 09:01:28 GMT
FROM:    I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg@iaa.es>

I. Perez-Garcia (IAA-CSIC), Y.-D. Hu (GXU), A. J. Castro-Tirado (IAA-CSIC), C.-Y. Dai (NJU), M. D. Caballero-Garcia, E. Fernandez-Garcia, M. Gritsevich, S. Guziy (IAA-CSIC), A. M. Garcia Rodriguez (GRANTECAN, IAC), on behalf of a larger collaboration, report:

We observed the optical afterglow of GRB 261113A (SVOM/ECLAIRs trigger sb26111302; Saccardi et al., GCN 46244) with the OSIRIS+ spectrograph on the 10.4m Gran Telescopio Canarias (La Palma, Spain). Long-slit spectra with the R1000B and R1000R grisms (600 s each, 1.23" slit) started on 2026 November 13 at 22:02 and 22:13 UT, i.e. about 7.5 hr after the trigger, with the slit centred on the optical/NIR counterpart (Lin et al., GCN 46247; Lei et al., GCN 46248; Li et al., GCN 46249; Yin et al., GCN 46250; Chen et al., GCN 46251; Wu et al., GCN 46252; Zhao et al., GCN 46253; Li et al., GCN 46254; Saikia et al., GCN 46256; Adami et al., GCN 46257; Gress et al., GCN 46258; Izzo et al., GCN 46259; Brivio et al., GCN 46260; Maksut et al., GCN 46262; Moskvitin et al., GCN 46263).

The afterglow is clearly detected (~21.7 AB at 6250 A within the slit). The spectrum shows:

- a damped Lyman-alpha absorption with zero flux between 5530 and 5570 A; a preliminary fit to its red wing gives log N(HI) ~ 21.4;
- the Lyman-alpha forest blueward of it, and no flux below ~4200 A, which is the Lyman limit at this redshift;
- C II 1334 absorption (blended with C II* 1335) at 6113.5 A.

These features give a redshift of z = 3.58, which confirms the VLT/X-shooter value (z = 3.580; Saccardi et al., GCN 46261).

A detailed analysis is ongoing.

We thank the GTC staff for their excellent support.