TITLE: GCN CIRCULAR NUMBER: 35398 SUBJECT: GRB 231216A: 10.4 m GTC optical upper limit DATE: 23/12/18 15:52:04 GMT FROM: Youdong HU at IAA-CSIC <huyoudong072@hotmail.com> Y.-D. Hu, R. Sanchez-Ramirez, A. J. Castro-Tirado, S. Guziy, M.D. Caballero-Garcia, S.-Y. Wu, E. Fernandez-Garcia, and I. Perez-Garcia (IAA-CSIC), F. Pérez-Toledo (GTC, IAC), S. B. Pandey (ARIES) and B.-B. Zhang (NJU) on behalf of a larger collaboration, report: Following the detection of GRB 231216A by Swift (Sbarrato et al., GCNC 35378), we triggered the 10.4m Gran Telescopio de Canarias (GTC) equipped with Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) in La Palma (Spain), starting on Dec 16, 20:18 UT (~1.7 h after the trigger). No optical afterglow is indentified within the refined Swift/XRT posiion (Sbarufatti et al. GCNC 35391) which down to i>24.5 mag, which is consistent with these reports from UVOT (Kuin et al., GCNC 35388), MASTER (Lipunov et al. GCNC 35379), NOT (Malesani et al. GCNC 35382), GIT (Sharma et al. GCNC 35383), T120 (Basa et al. GCNC 35384), REM (Ferro et al. GCNC 35389), AST-3 (Sun et al. GCNC 35390), Nastro Verde Observatory (Ruocco et al. GCNC 35394), LCOGT (Strausbaugh et al. GCNC 35395) and Nanshan/HMT (An et al. GCNC 35396). We thank the staff at GTC for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/35398. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...