TITLE: GCN CIRCULAR NUMBER: 29132 SUBJECT: Short GRB201221D: High Redshift from OSIRIS/GTC DATE: 20/12/22 14:49:53 GMT FROM: Alexander Kann at IAA-CSIC A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann (HETH/IAA-CSIC), L. Izzo (DARK/NBI), C.C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC) and G. Lombardi (GRANTECAN, IAC) report: We obtained spectroscopy of the optical counterpart (Malesani et al., GCN #29117) of the short GRB 201221D (Page et al., GCN #29112) with OSIRIS at the 10.4m Gran Telescopio Canarias (Roque de los Muchachos Observatory, La Palma, Spain), starting at 1:52 UT (2.757 hr after the burst). The observation consisted of 4 x 1200 s exposures with the R1000B grism, covering the range between 3700 and 7800 Angstrom. The spectrum shows a weak continuum over the full spectral range. There is a prominent emission feature that we identify as the [OII] 3727/3729 doublet at a redshift of 1.046. This line happens to lie in the atmospheric A band, and therefore must be quite strong to be detectable. There are also low significance absorption featuress coincident with FeII and MgII at a similar redshift (z = 1.045). We identify this as the redshift of GRB 201221D. We note this is a high redshift for a short GRB, and it represents one of the few short GRB spectra to show afterglow absorption features.