TITLE:   GCN CIRCULAR
NUMBER:  30976
SUBJECT: GRB 211023B: BOOTES-4/MET and 1.5m OSN optical upper limit
DATE:    21/10/24 20:31:50 GMT
FROM:    Youdong HU at IAA-CSIC  <huyoudong072@hotmail.com>

Y.-D. Hu, V. Casanova, T.-R. Sun, A. J. Castro-Tirado, M. D. Caballero-Garcia, M. A. Castro Tirado, E. Fernandez-Garcia (IAA-CSIC), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), S. Guziy (Univ. of Nikolaev) and D. R. Xiong, Y. F. Fan, J. M. Bai, C. J. Wang, Y. X. Xin, X. H. Zhao (Yunnan Observatories of CAS) on behalf of a larger collaboration, report:

Following the detection of GRB 211023B by Swift (S. Dichiara et al. GCNC 30960), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically respond to this burst starting on Oct 23 at 21:06:20 UT (~28 sec after trigger). Due to technical problems, the useful images were obtained only after 21:18:39 UT (~13 min after trigger). The optical afterglow reported by Swift/UVOT (S. Dichiara et al. GCNC 30960, N. P. M. Kuin et al. GCNC 30975) is not detected in the co-added image (10s x 30, clear filter) down to 19.9 mag.

We then triggered the 1.5m OSN telescope in Sierra Nevada Observatory (Granada, Spain) on Oct. 24 03:20 UT (~6.2 hrs after trigger). A series of image were taken in R and I -bands (300s exposures each filter). The optical afterglow is not detected in the co-added image (300s x 12) down to 21.6 mag (R-band).

These non-detections are consistent with the reports by MASTER (Lipunov et al. GCNC 30964), TSHAO (Pozanenko et al. GCNC 30972) and RATIR (Watson et al. GCNC 30973).

We thank the staff at Lijiang observatory and OSN for their excellent support.