GRB 240910A: Redshift from OSIRIS+/GTC

We observed the afterglow (Julakanti et al. GCN 37459; D'Ai et al. GCN 37461; Malesani et al. GCN 37463) of the long GRB 240910A, detected by Fermi (Fermi team, GCN 37441), SVOM (Zhang et al. GCN 37445) and GRBAlpha (Ripa et al. GCN 37450) using OSIRIS+ mounted on the 10.4 m GTC telescope, at the Roque de los Muchachos Observatory (La Palma, Spain). The observation consisted in 3 acquisition images in r-band, followed by 3x1200 s spectra, with grism R1000B, covering the spectral range between 3650 and 7800 AA at a resolving power of 600. The spectra were obtained at a mean epoch 2024-09-12T03:39:07 UT, 1.985 days after the Fermi trigger. The continuum is well detected in the complete spectral range and there are multiple features of CIV, FeII, AlII, AlIII, ZnII, MnII, MgII, MgI at a common redshift of z = 1.460, which we propose as the redshift of the GRB.