TITLE: GCN CIRCULAR NUMBER: 32742 SUBJECT: MAXI GRB 221006A: Redshifts of the possible host galaxies DATE: 22/10/13 19:01:48 GMT FROM: C. C. Thoene at HETH/IAA-CSIC P. A. C. Cunha (Univ. do Porto/CAUP), G. Ma (DAWN/NBI), R. O’Rourke Brogan (AIP), C. C. Thoene (ASU-CAS), A. de Ugarte Postigo (OCA, Nice), D. A. Kann (Goethe Univ.), J. F. Agui Fernandez (IAA-CSIC), L. Izzo (DARK/NBI), J.P.U. Fynbo (DAWN/NBI), N. R. Tanvir (Univ. Leicester), M. Blazek (Prague) and D. Garcia Alvarez (GTC) report: We observed the possible host galaxies of the MAXI GRB (GCN 32626, Mikhara et al) underlying the candidate afterglow at RA 22:28:58.99, DEC +15:42:49.6 (GCN 32628, Sbarufatti et al., confirmed to be fading in GCN 32731, Sbarufatti et al.), which we already reported in GCN 32710, (O’Rourke Brogan et al.). Observations were obtained with OSIRIS at the 10.4m GTC telescope in La Palma starting on Oct. 10, 2022 at 20:10 UT with a total exposure time of 3x600s using the R1000R grism (5100-10100Å) and a 1 arcsec slit aligned across both putative hosts. We clearly detect the traces of both galaxies in the combined spectrum and determine redshifts of z=0.731 for G1 and z=0.464 for G2 based on emission lines of [OII], [OIII] Hb and Ha. Based on the distance from the X-ray afterglow candidate we determined G1 to be the likely host of GRB 221006A (GCN 32710, O’Rourke Brogan et al.) and hence assume a redshift of z=0.731 for its possible host galaxy. We acknowledge two very enjoyable weeks at the NEON observing school during which these follow-up observations were obtained.