TITLE: GCN CIRCULAR NUMBER: 30856 SUBJECT: GRB 210919A: LOAO and LSGT optical upper limits DATE: 21/09/20 08:00:38 GMT FROM: Sophia Kim at Seoul National U. <sophiak@astro.snu.ac.kr> GRB 210919A: LOAO and LSGT optical upper limits Sophia Kim (Seoul National University, SNU), Myungshin Im (SNU); Jeff Cooke (Swinburne University of Technology), Gu Lim (SNU); report on behalf of IMSNG & GECKO Collaboration We carried out follow-up observations of GRB210919A (A. Tohuvanohu et al. GCNC #30846) with the 1-m telescope at Mt. Lemon Optical Astronomy Observatory (LOAO) in US Arizona. Observations began on September 19 at 10:42:02 UT , ~10.23 hours after the GRB trigger. We took 19 X 180s exposures in Johnson R-band. We also observed the same field with the 0.43-meter (17 inch) Lee Sang Gak Telescope (LSGT) located at the Siding Spring Observatory (SSO) in Australia. Imaging began on the same day at 16:12:53 UT, ~15.73 hours after the GRB trigger. The observations were performed in a Sloan r-, i- and z-band sequences with 11 X 300s exposures in each band. No GRB optical counterpart was found in the LOAO and LSGT data within the XRT error area (M. R. Goad et al. GCNC #30850). This result is consistent with the optical observational results by other teams (V. Lipunov et al. GCNC #30847, Y.-D. Hu et al. GCNC #30848, R. Strausbaugh et al. GCNC #30849, M.R. Goad et al. GCNC #30850, N. Pankov et al. GCNC #30851, D. A. Perley et al. GCNC #30852, M. Perri et al. GCNC #30854 and Y.Takamatsu et al. GCNC #30855). The following is our observation results. We calibrated flux with the PS1 catalog and used AB magnitude system. (The magnitudes are not corrected for extinction.) #-------------------------------------------------------------------------------------------------------------- OBS/TEL DATE-OBS(UT) FILTER EXPT UL(3σ)[ABmag] UL(5σ)[ABmag] LOAO/1-m 2021-09-19T10:42:02 R 3420s >21.716 >21.162 SSO/LSGT 2021-09-19T16:12:53 r 3300s >20.160 >19.605 SSO/LSGT 2021-09-19T16:18:17 i 3300s >19.107 >18.553 SSO/LSGT 2021-09-19T16:23:53 z 3300s >18.674 >18.119 -------------------------------------------------------------------- Sophia Kim Graduate Course, Astronomy Program, Dept. of Physics & Astronomy, Seoul National University 56-1 San, Shillim-dong, Kwanak-gu, Seoul, KOREA mobile: *+82-10-2668-3783* e-mail : *sophiak@astro.snu.ac.kr <sophiak@astro.snu.ac.kr>*