TITLE: GCN CIRCULAR NUMBER: 29805 SUBJECT: GRB 210410A: MITSuME Akeno optical upper limits DATE: 21/04/12 10:29:30 GMT FROM: Katsuhiro L. Murata at Nagoya U K. L. Murata, R. Hosokawa, M. Niwano, N. Ito, H. Takamatsu, Y. Yatsu, and N.Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the field of GRB 210410A (The Fermi GBM team et al. GCN Circular #29777, A. Melandri et al. GCN Circular #29778, V. Lipunov et al. GCN Circular #29779, M. Jelinek et al. GCN Circular #29780, M. Arimoto et al. GCN Circular #29781, A. Ursi et al. GCN Circular #29782, Nat Butler et al. GCN Circular #29784, Nat Butler et al. GCN Circular #29786, Paul Kuin et al. GCN Circular #29787, J. Wood et al. GCN Circular #29788, A. D'Ai et al. GCN Circular #29790, A. Y. Lien et al. GCN Circular #29793, A. Ridnaia et al. GCN Circular #29797, A. Ursi et al. GCN Circular #29798) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation with a series of 60 sec exposures started at 2021-04-10 13:35 (9.7 hours after the Fermi/GBM trigger). We stacked the images with good conditions. We did not detect the optical afterglow reported previously (Jelinek et al. GCN Circular #29780, Butler et al. GCN Circular #29784) in all three bands. We obtained the 5-sigma limits of the stacked images as follows. T0+[hour] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ 10.0 14:00:15 1740 g'>19.3, Rc>19.6, Ic>19.0 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used the PS1 catalog for flux calibration.The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).