GCN Circular 30992

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.