TITLE: GCN CIRCULAR NUMBER: 30992 SUBJECT: Possible Short GRB 211023B: CAHA 2.2m Detection DATE: 21/10/25 14:56:49 GMT FROM: Alexander Kann at IAA-CSIC <kann@iaa.es> D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), A. Guijarro, and P. Martin-Fernandez (both CAHA) report: We observed the optical afterglow of the potentially short Swift GRB 211023B (Dichiara et al., GCN #30960; Kuin & Dichiara, GCN #30975) with CAFOS mounted on the 2.2m Telescope at Calar Alto, Almeria, Spain. We obtained 30 x 90 s in the SDSS i' band under mediocre conditions. At the position of the GRB afterglow discovered by Swift/UVOT (Kuin & Dichiara, GCN #30975), we detect a source. Against two Pan-STARRS comparison stars, we measure: i' = 22.26 +\- 0.10 mag (AB) at 0.3091 d after the GRB. We note this faint magnitude is in agreement with both earlier (Lipunov et al., GCN #30964; Pozanenko et al., GCN #30972; Yu et al., GCN #30976), simultaneous (Yu et al., GCN #30976), and later (Watson et al., GCN #30973) non-detections.