TITLE:   GCN CIRCULAR
NUMBER:  35598
SUBJECT: GRB 240122A: Redshift from OSIRIS+/GTC
DATE:    24/01/23 01:06:27 GMT
FROM:    Christina Thöne at ASU-CAS <christina.thoene@gmail.com>

C. C. Thoene (ASU-CAS), A. de Ugarte Postigo (CNRS/OCA and LAM), J. F. Agui Fernandez (CAHA), L. Izzo (INAF/Capodimonte), J. P. U. Fynbo (DAWN/NBI), N. R. Tanvir (U. Leicester), M. Blazek (CAHA), S. Geier, A. Garcia-Rodriguez, Miguel Rivero Mendez (both GTC) report: 

We obtained spectroscopy of the optical afterglow (Kumar et al. GCN 35596) of the MAXI/GSC GRB 240122A (Negoro et al. GCN 35593) with OSIRIS+ at the 10.4m GTC at a mean epoch of 0.5357 days after the GRB. The observation consisted of 3x900s exposures using grism R1000B, which covers the range between 3700 and 7780 AA at a resolving power of about 600. The observation was strongly impacted by the nearby Moon and poor seeing.

A preliminary reduction of the spectrum shows a continuum with multiple absorption features. We determine the redshift of the GRB indentifying Lyman alpha and Lyman beta as well as absorption features of SiII, SiIV, CI, CII, CIV and FeII at a common redshift of z=3.162. We note that the Lyman series is rather weak compared to typical GRB  sight lines.