GRB 241029A: GTC/OSIRIS+ spectroscopic redshift z=1.072

We observed the afterglow of GRB 241029A (Fermi GBM team, GCN 37932; Schanne et al., GCN 37934; Chenwei Wang et al., GCN 37935; Evans et al., GCN 37936; Jiang et al., GCN 37937; Weikang Lin et al., GCN 37939; Jiang et al., GCN 37940; Francile et al., GCN 37941; Ackley et al., GCN 37943; Odeh et al., GCN 37944; Myers et al., GCN 37945; Bernardini et al., GCN 37946, Adami et al., GCN 37948) using OSIRIS+ on the 10.4 m GTC telescope, at the Roque de los Muchachos Observatory (La Palma, Spain). The observation consisted of 4 acquisition images in r-band, followed by a 4x1200 s spectrum. The spectrum was obtained with grism R1000B, covering the spectral range between 3650 and 7800 AA at a resolving power of 600. The acquisition image, obtained at 2024-10-29T21:32:51 UT, 19.21 hr since the Fermi trigger, shows the afterglow at r(AB) = 21.40 +/- 0.04 mag, as compared to SDSS field stars. The spectrum has a strong continuum throughout the complete range with absorption features due Fe II, FeII*, Mn II, Mg II, Mg I and the [O II] doublet at z = 1.072, which we propose as the redshift of GRB 241029A.