TITLE:   GCN CIRCULAR
NUMBER:  30909
SUBJECT: GRB 210930A: CAHA 2.2m telescope optical limit
DATE:    21/10/01 04:35:31 GMT
FROM:    Youdong HU at IAA-CSIC  <huyoudong072@hotmail.com>

Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia, A. J. Castro-Tirado, M. D. Caballero-Garcia, R. Sanchez-Ramirez, M. A. Castro Tirado (IAA-CSIC) and I. Vico (CAHA) on behalf of a larger collaboration, report:

Following the detection of GRB 210930A by Swift (V. D'Elia et al. GCNC 30897), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). Images were gathered after the twilight starting on Sep. 30 18:56:50 UT (i.e. 16.2 hour post trigger) in Sloan-gri bands with 90 s exposure each. On the co-added r-band image (6x90s), no optical transient down to 22.6 mag is detected at the X-ray afterglow candidate position reported by Swift/XRT (V. D'Elia et al. GCNC 30897, J.P. Osborne et al. GCNC 30900). This non-detection is consistent with the report from A. Belles et al. (GCNC 30903) and V. Lipunov et al.(GCNC 30901).

We thank the staff at Calar Alto observatory for their excellent support.